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THE  IOWAN  DRIFT 

A  Review  of  the  Evidences  of  the  lowan 
Stage  of  Glaciation 


A  GO-OPERATIVE  STUDY  FOR  THE  U.  S.  GEOLOGICAL  SURVEY 
AND  THE  IOWA  GEOLOGICAL  SURVEY 


BY 

WILLIAM  C.  ALDEN,  Ph.  D. 

U.  S.  Geological  Survey 
AND 

MORRIS  M.  LEIGHTON,  M.  S. 

Iowa  Geological  Survey 


A   DISSERTATION 

SUBMITTED  TO  THE  FACULTY  OF  THE  OGDEN  GRADUATE 
SCHOOL  OF  SCIENCE  IN  THE  CANDIDACY  OF  MR.  LEIGHTON   FOR 
THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 

DEPARTMENT   OF  GEOLOGV  AND  PALEONTOLOGY 


Private  Edition,  Distributed  By 

THE  UNIVERSITY  OF  CHICAGO  LIBRARIES 

CHICAGO,  ILLINOIS 


Reprinted  from 

IOWA  GEOLOGICAL  SURVEY 

VOLUME  XXVI,  ANNUAL  REPORT  FOR  1915 

Des  Moines,  1917 


THE  IOWAN  DRIFT,  A  REVIEW  OF 

^THE  EVIDENCES  OF  THE  IOWAN 

STAGE  OF  GLAGIATION 

BY 

WM.  G.  ALDEN  and  MORRIS  M.  LEIGHTON 


PREPARED  IN  COOPERATION  WITH  THE  UNITED  STATES  GEOLOGICAL  SURVEY 


ERRATA 


PAGE  57.  Lnder  "Pleistocene  Deposits":  statements  2,  4  and  8  should 
be  indented  like  6,  and  5  should  be  flush  with  7,  so  as  to  be  consistent  with 
the  preceding  list  of  events  under  "Pleistocene  Epoch." 

PAGE  86,  FIG.  4.  To  conform  with  the  text,  the  letters  a,  b  and  b' 
should  be  inserted  in  the  figure  as  follows:  a  at  the  heavy  line  in  the  right 
part  of  the  diagram  which  inHiV?it/»c  »tm  f^^^^  — i  i — L_J  <_  /•>•.•,. 
calcareous  buff  till;  b  at  the 
calcareous  loess  and  the  calca 
in  the  left  half  of  the  diagram. 


should  be  inserted  in  the  figure  as  follows:  a  at  the  heavy  line  in  the  right 
part  of  the  diagram  which  indicates  the  ferretto  and  leached  buff  till  on 
cacareous  buff  till;  b  at  the  line  of  contact  just  to  the  left,  between  the 
calcareous  loess  and  the  calcareous  till;  and  b'  at  the  same  line  of  contact 
in  the  left  half  nt  thf>  Hiatrrom 


Qft-n ' 


CONTENTS 


Introduction    55 

Character  of  the  investigation  and  general  results 55 

Chapter  I.    The  lowan  drift 60 

Distribution  and  configuration  in  Iowa 60 

Area    60 

Topography 60 

Chapter  II.     The  uppermost  till  of  the  lowan  area 77 

The  lithology  of  the  lowan  drift  and  its  comparison  with  other  drifts. .     79 

The  oxidation  of  the  till  •  • 80 

The  effects  of  leaching 81 

The  overlying  loesslike  clay 83 

Comparison  with  the  Kansan  till 83 

The  oxidation  of  the  Kansan  drift 83 

The  leaching  of  the  Kansan  drift 85 

Comparison  with  the  Wisconsin  till 88 

Chapter  III.     The  super-Kansan  "gumbo" 89 

In  the  Kansan  drift  area .89 

In  the  lowan  drift  area 92 

Jones  County   93 

Delaware  County    95 

Buchanan  County   96 

Linn  County  97 

Benton  County .     98 

Black   Hawk   County 99 

Fayette  County   100 

Howard  County  101 

Mitchell    County 102 

Worth  County   104 

Cerro  Gordo  County 104 

Franklin  County 104 

Tama  County • 105 

Chapter  IV.    Other  evidences  of  post-Kansan  glaciation 110 

General  character  110 

Winneshiek  County   110 

Howard  County Ill 

Chickasaw  County   Ill 

Buchanan  County   112 

Linn  County  115 

Jones  County  116 

Johnson   County 117 

Chapter  V.     Bowlders , . . 121 


52  CONTENTS 

Character  and  size 121 

Distribution  within  the  lowan  area 122 

Geographically 122, 

Topographic  distribution 125 

Character  of  embedding  till 126 

Bowlders  in  the  Kansan  area. .  •  • 126 

Big  bowlde'rs  as  evidence  of  lowan  glaciation 127 

Chapter  VI.     lowan  outwash  and  other  gravels 130 

Valley   train    terraces 130 

State  of  weathering 1S6 

Absence  of  glacio-fluvial  gravel  in  certain  valleys  of  the  Kansan  area.  .  \'-ll 

Upland  gravel 137 

lowan  karr.es 138 

Kansan  kames   138 

Comparison  with  gravels  of  Wisconsin  age 139 

Summary    139 

Chapter  VII.     The  loess  and  its  significance 140 

General  characters   140 

The  fossil  content  and  its  significance 141 

Modification  of  the  loess  by  weathering 142 

Distribution  of  the  loess 144 

Conclusion  as  to  sources  of  the  loess 153 

Stratigraphic  relations  of  the  loess 154 

To  the  Kansan  drift. 154 

To  the  Illinoian  drift. .  -  - 154 

Relations  to  the  lowan  drift 156 

Relations  to  the  Wisconsin  drift 158 

Summary 162 

Conclusions  from  relations  of  the  loess 164 

Chapter  VIII.     The  age  of  the  lowan  drift 164 

Chapter  IX.    Border  phenomena  and  limits  of  the  lowan  drift 171. 

Appendices    181 

A.     Tables  of  estimates  cf  litholosic  composition  of  the  drift 181 

1.  Estimates  of  pebbles  frcm  unleached  Wisconsin  drift 182 

2.  Estimates  of   pebbles   -ron   unleached   part  of  uppermost  till, 

or  lowan,  of  the  'lowan  area 183 

3.  Estimates  of  pebbles  from  leached  part  of  uppermost  till,  or 

lowan,  of  the  lowan  area 184 

4.  Estimates  of  pebbles  from  Buchanan(?)  gravel  in  lowan  area. .  135 

5.  Estimates  of  pebbles  from  unleached  Kansan  (?)   till  of  lowan 

area 186 

6.  Estimates  of  pebbles  from  the  leached  and  oxidized  upper  part 

of  the  Kansan  till  outside  of  lowan  area 187 

7.  Estimates  of  pebbles  from  the  unleached   Kansan  till  outside 

of  lowan  area  188 

8.  Estimates  of  pebbles  from  Aftonian  gravels 189 

9.  Estimates  of  pebbles  from  sub-Aftonian,  or  Xebraskan,  till 189 


CONTENTS  53 

B.  Notes  on  exposures  of  super-Kansan  "gumbo,"  in  the  Kansan  drift 

area    190 

Story  County    •  • '. . . 190 

Marshall  County   190 

Poweshiek  County 192 

Iowa  County  193 

Washington  County    194 

Johnson  County 195 

Cedar  County 195 

Clinton  County    196 

Jones  County   197 

Scott  County    198 

Rock  Island  County,  Illinois 198 

Gumbo  beneath  Illinoian  till 198 

Louisa  County,  Iowa 198 

Henry  County,  Illinois 198 

C.  Occurrences  of  drift,  possibly  lowan 200 

Winneshiek  County    200 

Cerro  Gordo  County : 200 

Floyd  County   201 

Chickasaw  County 201 

Bremer  County    201 

Fayette  County 202 

Delaware  County 208 

Buchanan  County   208 

Black  Hawk  County 210 

Benton  County  210 

Linn  County 211 

Jones  County   212 


THE  IOWAN  DRIFT 

A  REVIEW  OF  THE  EVIDENCES  OF  THE  IOWAN  STAGE  OF  GLACIATION 


Introduction 

CHARACTER  OF  THE  INVESTIGATION  AND  GENERAL  RESULTS 

b'or  many  years  northeastern  Iowa  has  been  a  region  of  great 
interest  to  students  of  Pleistocene  geology  and  many  papers 
have  been  published  treating  of  its  various  features.  Differen- 
t;ation  of  the  deposits  as  the  product  of  several  distinct  ice  in- 
vasions may  be  said  to  have  begun  with  the  tracing  of  the  limits 
of  the  drift  of  the  Des  Moines  lobe  of  the  last  ice  sheet  as 
distinguished  from  older  drift  in  the  area  outside.  Later  the 
United  States  Geological  Survey  published  W  J  McGee's  paper 
on  the  Pleistocene  of  northeastern  Iowa,1  in  which  he  showed 
that  there  were  two  drift  sheets  in  this  part  of  the  state  which 
were  older  than  the  drift  of  the  Des  Moines  lobe.  Still  later  the 
Iowa  Geological  Survey,  with  the  late  Dr.  Samuel  Calvin  at  its 
head,  reached  the  conclusion  that  instead  of  two  drift  sheets 
there  were  really  three  in  northeastern  Iowa,  each  the  product 
of  a  distinct  ice  advance  prior  to  the  incursion  of  the  Des  Moines 
lobe.  The  progress  of  the  investigations  necessitated  certain 
changes  in  the  classification  and  the  shifting  of  names  to  desig- 
nate the  deposits.  It  is  not  necessary  to  consider  in  this  place 
these  changes  in  the  nomenclature  nor  the  merits  of  such  adjust- 
ments as  were  made.  The  elaboration  of  the  remarkable  Pleis- 
tocene classification  that  resulted  from  these  and  correlated 
studies  called  for  close  scrutiny  of  the  evidence  and  almost 
inevitably  differences  of  opinion  arose  concerning  some  of  its 
features.  Skepticism  centered  principally  on  the  lowan  drift, 
said  to  be  the  product  of  the  fourth  great  glacier  which  had 
invaded  the  area  of  the  state  or  the  third  which  spread  over 

1McGee,  W  J,  The  Pleistocene  of  northeastern  Iowa:  U.  S.  Geol.  Survey  Eleventh 
Ann.  Kept,  pt.  1,  pp.  189-577,  1891. 


56  THE   IOWAN   DRIFT 

northeastern  Iowa.  This  skepticism  arose  very  largely  because 
of  difference  of  opinion  as  to  the  interpretation  to  be  given 
certain  of  the  phenomena  observed.  This  was  expressed  par- 
ticularly in  several  papers  published  by  Frank  Leverett  of  the 
United  States  Geological  Survey.  In  defense  of  the  lowan  drift 
a  number  of  papers  were  published  by  Doctor  Calvin.  The 
discussion  had  to  do  principally  with  two  questions:  (1)  Is 
there  really  in  northeastern  Iowa  a  drift  sheet  of  pre-Wisconsin 
age  distinct  from,  and  younger  than,  the  Kansan  drift?  and 
(2)  If  so,  is  it  to  be  correlated  with  the  Illinoian  drift  sheet 
(of  Leverett),  or  was  it  the  product  of  a  distinctly  later  ice 
invasion?  The  matter  was  still  in  question  at  the  time  of  Doctor 
Calvin's  death  in  1911.  There  being  a  desire  for  a  review  of 
the  evidence  bearing  on  the  lowan  problem,  Doctor  Calvin's 
successor,  the  present  State  Geologist,  Dr.  George  F.  Kay, 
finally  requested  the  United  States  Geological  Survey  to  co- 
operate with  the  Iowa  Survey  in  an  investigation  of  the  matter. 
An  agreement  was  reached  and  the  senior  author  of  this  report 
was  assigned  to  this  work  by  the  Federal  Survey  with  Morris 
M.  Leighton  of  the  Iowa  Survey  as  assistant. 

The  summer  seasons  of  1914  and  1915  were  spent  on  the  field 
investigations  besides  careful  study  of  the  published  and  un- 
published material  in  the  office.  It  is  a  pleasure  to  report  that 
the  conclusion  has  been  reached  that  there  is  what  seems  to  the 
writers  to  be  good  evidence  of  the  presence  of  a  post-Kansan 
drift  sheet  in  northeastern  Iowa  and  that  this  drift  appears  to 
be  older  than  the  Wisconsin  and  younger  than  the  Illinoian 
drift.  The  writers  are,  therefore,  in  the  main  in  agreement 
with  the  late  State  Geologist,  Dr.  Samuel  Calvin,  in  regard  to 
the  lowan  drift.  There  is,  therefore,  warrant  for  continued  use 
of  lowan  drift  and  lowan  stage  of  glaciation  as  major  sub- 
divisions of  the  Pleistocene  classification.  This  classification  is 
as  follows: 

PLEISTOCENE  EPOCH. 

9.  Wisconsin  stage  of  glaciation  (of  Chamberlin) 

8.  Peorian  stage  of  deglaciation  (of  Leverett) 

7.  lowan  stage  of  glaciation  (of  Iowa  geologists) 

6.  Sangamon  stage  of  deglaciation  (of  Leverett) 


PLEISTOCENE    DEPOSITS   IN   IOWA  57 

5.     Illinoian  stage  of  glaciation  (of  Leverett) 

4.    Yarmouth  stage  of  deglaciation  (of  Leverett) 

3.  Kansan  stage  of  glaciation  (of  Iowa  geologists) 

2.    Aftonian  stage  of  deglaciation  (of  Chamberlin) 

1.  Nebraskan  stage  of  glaciation  (of  Iowa  geologists)   (pre- 
Kansan  of  Chamberlin)    (Jerseyan    of    eastern    United 
States) 

These  subdivisions  of  Pleistocene  time  are  represented  in 
Iowa  by  the  following: 

PLEISTOCENE  DEPOSITS. 

9.     Wisconsin  drift  (of  the  Des  Moines  lobe) 

(b)     Peorian  soil  and  weathered  .zone  (of  Leverett) 

at  top  of  loess  and  beneath  Wisconsin  drift 
(a)     Main  deposit  of  loess2 
7.     lowan  drift  (of  Iowa  geologists) 

6.     Sangamon  soil,  vegetal  deposits,  and  weathered  zone 
(of  Leverett)   (including  super-Illinoian  " gumbo," 
or  "gumbotiP'of  Kay)  at  top  of  Illinoian  drift  and 
beneath  loess 
5.     Illinoian  drift  (of  Leverett) 

4.  Yarmouth  soil,  vegetal  deposits,  and  weathered  zone  (of 
Leverett)    (including  super-Kansan  " gumbo,"  or  "gum- 
botil"  of  Kay3)  at  top  of  the  Kansan  drift;  also  Buchanan 
gravel  (of  Iowa  geologists)  beneath  lowan  drift  and  loess 

3.     Kansan  drift  (of  Iowa  geologists) 

2.  Aftonian  gravels,  vegetal  deposits,   soil  and  weathered 
zone  (of  Chamberlin)  (including  super-Nebraskan  "gum- 
bo" or  "gumbotil"  of  Kay)  at  top  of  Nebraskan  drift 

1.  Nebraskan  drift  (of  Iowa  geologists)  (pre-Kansan  or  sub- 
Aftonian  of  Chamberlin) 

In  the  course  of  the  field  work  about  175  traverses  were  made 
in  and  adjacent  to  the  lowan  drift  area  and  a  large  number  of 
exposures  were  carefully  examined.  Fortunately,  many  new 
cuts  were  available  as  the  result  of  recent  grading  on  the  wagon 
roads  and  electric  and  steam  railways.  In  addition  about  250 

2Local  deposits  cf  loess  and  of  laminated  silts  occur  on  the  Wisconsin  and  older 
drift  sheets. 

3Kay,  Geo.  P..  Gumbotil.  a  new  term  in  Pleistocene  geo'.ogy:  Science,  new  ser., 
Vol.  XLIV,  pp.  637-638,  1916. 


58  THE  IOWAN   DRIFT 

borings  were  made  with  a  2-inch  auger  "8  feet  in  length.  The 
auger  was  used  principally  where  exposures  were  not  available, 
particularly  on  the  typical  lowan  plains  and  other  uplands 
Samples  obtained  thereby  were  carefully  examined  for  deter- 
mination of  the  character,  the  depth  of  leaching  and  degree  of 
oxidation  of  the  superficial  parts  of  the  drift.  Not  much  atten- 
tion was  given  to  the  collection  of  well  data,  reliance  being  placed 
on  the  statements  in  the  reports  of  the  Iowa  Survey  for  the 
thickness  of  the  drift. 

Many  examinations  for  purposes  of  comparison  were  made 
outside  the  lowan  drift  area  in  the  Kansan  and  Illinoian  drift 
areas  in  Iowa  and  by  Mr.  Alden  on  the  Illinoian  drift  in  Illinois. 
Besides  these,  a  number  of  reconnaissance  trips  were  made  by 
Mr.  Alden  in  the  area  outside  the  Wisconsin  terminal  moraine 
in  southeastern  Minnesota.  Some  of  these  were  in  company 
with  one  or  two  of  the  following  gentlemen,  Frank  Leverett, 
F.  W.  Sardeson,  and  Samuel  Weidman.  The  writers  are  espe- 
cially indebted  to  T.  C.  Chamberlin,  R.  D.  Salisbury,  George  F. 
Kay  and  Frank  Leverett.  Conferences  were  had  also  with 
Wm.  H.  Norton,  R.  T.  Chamberlin,  J.  E.  Carman,  A.  C.  Trow- 
bridge,  A.  0.  Thomas  and  J.  A.  Williams. 

In  connection  with  this  study  the  writers  were  fortunate  in 
having  access  to  the  field  notes  of  the  late  Doctor  Calvin,  to  an 
unpublished  manuscript  by  Mr.  Leverett,  to  some  notes  by 
T.  C.  Chamberlin  on  field  conferences  in  Wisconsin,  Minnesota, 
and  Iowa,  and  to  field  notes  of  R.  T.  Chamberlin  on  his  studies 
in  1906  and  1907  of  the  drift  in  southern  and  eastern  Iowa, 
southeastern  Minnesota  and  northwestern  Wisconsin,  for  the 
United  States  Geological  Survey.  In  the  course  of  these  latter 
studies  R.  T.  Chamberlin  made  many  estimates  of  the  lithologic 
composition  of  the  several  drift  sheets  by  the  counting  and 
sorting  of  pebbles.  Through  his  kindness  the  present  writers 
are  permitted  to  include  in  this  report  the  results  of  these 
estimates  together  with  the  results  of  similar  estimates  made 
by  themselves.  They  are  compiled  in  the  tables  presented  in 
Appendix  A. 

The  writers  are  indebted  to  R.  D.  Salisbury  for  examina- 
tion and  criticism  of  a  preliminary  draft  of  the  manuscript, 


SCOPE  OF  INVESTIGATION  55) 

and  Prank  Leverett  and  F.  W.  Sardeson  also  very  kindly 
examined  and  criticised  the  manuscript  of  this  report.  They 
are,  however,  in  no  way  responsible  for  the  interpretations 
presented.  To  all  these  gentlemen  the  writers  wish  to  express 
their  appreciation. 

As  stated  above,  the  investigation  has  yielded  what  seems  to 
the  writers  to  be  good  evidence  of  a  post-Illinoian  and  pre- 
Wisconsin  glaciation  of  northeastern  Iowa.  There  may,  of 
course,  be  room  for  differences  of  opinion  as  to  some  of  the 
interpretations.  Were  the  phenomena  entirely  clear  and  deci- 
sive the  question  would  not  so  long  have  remained  open.  The 
evidence  is  not,  however,  like  a  chain  whose  maximum  strength 
is  that  of  the  weakest  link,  but  may  rather  be  likened  to  a  rope 
composed  of  strands  none  of  which  alone  may  be  able  to  support 
the  burden  but  whose  combined  pull  in  the  same  direction  brings 
conviction. 

Inasmuch  as  this  paper  is  intended  primarily  as  a  review  of 
the  evidence  rather  than  as  an  argument  in  favor  of  the  lowan 
stage  of  glaciation  the  effort  has  been  made  to  bring  together 
about  all  the  available  data  bearing  on  the  question.  Some  of 
the  less  important  details  have  been  put  in  the  appendices. 
Some  of  these  have  little  value  as  evidence  and  some  may  not 
appear  to  be  pertinent.  Quite  a  number  of  different  persons 
have  studied  the  Pleistocene  geology  of  this  region  and  nu- 
merous supposed  occurrences  of  lowan  drift  have  been  cited,  so 
that  it  has  seemed  best  to  take  cognizance  of  data  published 
even  though  some  of  it  may  not  now  appear  very  important. 

It  has  been  thought  not  to  be  necessary  to  present  in  this  paper 
a  detailed  discussion  of  the  history  and  development  of  the 
classification  of  the  Pleistocene  deposits  of  Iowa.  There  are 
in  the  text  numerous  references  to  earlier  publications  of  various 
writers,  but  no  bibliography  or  review  of  papers  treating  of  the 
lowan  drift  is  presented.  For  reference  to  these  papers  readers 
should  consult  the  annotated  bibliography  of  Iowa  geology  and 
mining  by  Charles  Keyes,  volume  XXII,  Iowa  Geological  Sur- 
vey (1912)  or  the  several  bibliographies  of  North  American 
geology  published  by  the  United  States  Geological  Survey. 


60  THE   IOWAN  DRIFT 

CHAPTER  1 
THE  IOWAN  DRIFT. 

DISTRIBUTION  AND  CONFIGURATION    IN    IOWA. 

Area. — The  evidence  reviewed  in  this  paper  seems  to  the 
writers  to  indicate  that  a  post-Kansan  glaciation  (pre- Wisconsin 
and  post-Illinoian)  extended  over  that  part  of  northeastern 
Iowa  lying  between  the  east  boundary  of  the  Wisconsin  drift 
on  the  west  and  the  belt  of  thin  drift  bordering  the  Driftless 
Area  on  the  east.  The  drift  deposited  at  this  stage  is  the  lowan 
drift.  The  lowan  ice  sheet  may  also  have  covered  part  of 
southeastern  Minnesota,  but  the  writers  have  not  themselves 
examined  enough  of  that  area  to  warrant  its  discussion  in  this 
paper.  The  lowan  drift  in  Iowa  lies  principally  in  the  basins  of 
Cedar  and  Wapsipinicon  rivers.  The  eastern  part  is  drained  by 
the  headwaters  of  Upper  Iowa,  Turkey,  Volga,  and  Maquoketa 
rivers  and  some  of  the  southern  part  of  the  area  drains  to  Iowa 
river.  This  area,  more  than  9,000  square  miles,  is  larger  than 
Massachusetts  and  about  equal  to  New  Hampshire  or  Vermont, 
and  somewhat  less  than  Maryland. 

Topography. — Comparisons  of  surficial  configuration  and  oJ 
the  degree  of  modification  of  the  drift  by  erosion  have  generally 
been  among  the  criteria  for  discrimination  of  the  relative  age- 
of  different  drift  sheets  so  that  this  review  may  well  begin  with 
a  study  of  the  topography.  The  sort  of  topography  generally 
characteristic  of  this  part  of  northeastern  Iowa  is  somewhat 
peculiar  and  it  is  recognized  that  there  may  be  considerable 
difference  of  opinion  as  to  its  interpretation.  The  influence  of 
certain  factors  such  as  of  slope,  of  material  and  of  vegetal  cover, 
and  of  earlier  climatic  conditions,  are  not  readily  evaluated  and 
their  discussion  is  not  attempted  in  this  connection.  Such  study 
of  this  and  adjacent  areas  as  the  writers  have  made  in  the 
course  of  this  investigation  seems  to  them,  however,  to  show 
topographic  differences  which,  taken  in  connection  with  the 
other  data  here  presented,  are  significant  of  differences  in  the 
age  of  the  glacial  drift. 


FROM   U.  S.  G.  S.  TOPOGRAPHIC  MAP 

(KNOXVILLE  SHEET,   IOWA) 
R.  SOW. 


IOWA  GEOLOGICAL  SURVEY 
PLATE  I 


•  ™ 


TOPOGRAPHIC  MAP  OF  A  PORTION  OF  THE  DISSECTED 
KANSAN  TILL  PLAIN  IN  MARION  COUNTY,  IOWA 

Scale    6^,500 


C out OTU?  interval  2O  feet. 


TOPOGRAPHY  OF  IOWAN  AND  KANSAN  AREAS  61 

The  topography  of  the  lowan  area  is,  in  general,  what  the 
writers  would  call  a  mantled,  mature-erosion  type.  There  is 
not,  with  some  exceptions,  the  depositional  type  seen  in  the 
Wisconsin  drift  area  where  the  surface  configuration  is  largely, 
if  not  primarily,  due  to  the  irregular  deposition  of  the  drift, 
either  of  the  undulating  ground  moraine  type  or  the  sag-and- 
swell,  or  knob-and-kettle  morainal  type,  with  the  nearly  total 
obliteration  of  the  configuration  of  the  underlying  surface. 
In  the  lowan  area,  though  it  is  not  generally  dissected  by 
sharp-cut,  eroded  valleys,  there  are  yet  present  nearly  every- 
where the  main  features  of  maturely  branching  stream-erosion 
systems.  The  valleys  divide  and  sub-divide  in  dendritic  fashion 
and  their  branches  reach  most  parts  of  the  area.  Even  the 
more  nearly  flat  and  less  dissected  parts  show  this  drainage 
pattern. 

There  is  a  difference,  however,  between  this  topography  and 
that  of  most  of  those  parts  of  the  Kansan  drift  area  known  to 
the  writers.  In  the  latter  there  is  not  only  deep  dissection  but 
the  ramifications  of  the  branches  are  developed  in  minute  detail 
down  to  ravines  and  gullies  trenching  the  slopes  at  intervals  of 
a  few  rods.  Convex  curves  prevail  on  the  slopes  and  more  or 
less  sharply  cut,  V:shaped,  cross-profiles  predominate  except  in 
the  broader,  flat-bottomed  valleys. 

The  topography  of  the  Kansan  drift,  which  has  been  developed 
by  long  erosion  of  a  nearly  flat  drift  plain,  is  well  illustrated 
by  the  contours  on  Plate  I,  reproduced  from  a  part  of  the 
Knoxville  topographic  sheet.  This  is  one  of  the  newly  sur- 
veyed areas  and  the  dissected  topography  is  about  as  accurately 
reproduced  as  the  scale  of  the  map  permits.  There  is,  however, 
even  more  detailed  dissection  of  slopes  than  can  be  shown  on 
this  scale.  There  is  a  relief  of  100  to  200  feet  in  this  area  and 
only  narrow  remnants  of  the  original  plain  remain  as  uplands ; 
and,  as  seen  in  the  field,  it  would  be  noted  that  even  much  of 
the  upland  tracts  is  scarred  by  the  tips  of  the  erosion  lines. 

This  type  of  topography  and  degree  of  dissection  is  charac- 
teristic of  nearly  all  parts  of  the  Kansan  drift  area  which  have 
been  seen  by  the  writers.  The  same  is  illustrated,  by  Plates 
III  and  IV. 


62  THE   IOWAN   DRIFT 

In  the  lowan  drift  area,  while  the  main  features  of  the 
dendritic  branching  systems  are  present  the  minor  details  aije 
more  generally  lacking.  V-shaped  cross-  profiles  are  rarely  seen. 
The  side  slopes  are  long  and  of  low  grade  and  pass  at  the  bottom 
into  concave  curves.  The  minor  valleys  are  thus  broad  open 
swales  which  fade  out  indefinitely  into  nearly  flat,  interstream, 
upland  areas.  Though  these  valleys  are  quite  capacious  in  their 
lower  parts,  as  the  relief  ranges  from  30  to  150  feet,  the  slopes 
are  smooth  and  uncut,  or  very  little  cut,  by  ravines  and  gullies. 
One  looks  in  vain,  in  most  places,  for  the  smaller  branches  and 
twigs  of  the  dendritic  system.  The  present  streams  do  not 
appear  to  have  been  the  sole  agents  in  giving  the  valleys  their 
present  contours.  These  streams  meander  in  shallow  trenches 
cut  in  broad  bottoms  of  the  swales.  The  waters  from  the  valley 
slopes  appear  to  run  off  in  sheets,  so  to  speak,  rather  than  by 
gathering  into  converging  gullies  and  ravines.  One  looks  di- 
rectly down  open  troughs,  broad  and  relatively  shallow,  though 
often  of  considerable  actual  depth,  and  sees  the  slopes  in  large 
measure  unscarred  by  erosion  lines  and  not  made  irregular  by 
projecting  spurs. 

This  type  of  topography  is  fairly  well  illustrated  in  Plate  II 
\7hich  is  a  reproduction  of  parts  of  the  Marion  and  Anamosa 
topographic  sheets  on  the  same  scale  as  Plate  I.  This  shows 
a  part  of  the  typical  lowan  drift  plain.  It  should  be  noted  that 
this  is  from  the  older  and  less  accurate  of  the  topographic 
sheets.  Parts  of  this  older  set  of  maps  which  cover  maturely 
dissected  Kansan  drift  areas  to  the  east  of  the  lowan  drift 
a  rea  and  to  the  south  in  Cedar,  Johnson,  and  Iowa  counties,  do 
not  represent  the  dissected  topography  there  with  anything  like 
the  accuracy  of  detail  found  on  the  newer  maps.  This  is  true 
also  of  those  parts  of  the  older  maps  covering  Illinoian  drift 
ireas  in  Scott  and  Muscatine  counties,  so  that  comparisons 
should  not  be  made  of  the  contouring  of  the  typical  lowan 
topography  on  these  old  maps  with  that  of  the  Kansan  or 
Illinoian  topography  on  the  same  set  of  maps.  On  the  other 
hand,  critical  examination  in  the  field  shows  that  the  typical 
lowan  topography,  such  as  that  of  the  part  of  Linn  county 
shown  in  Plate  II  is  fairly  well  represented  by  the  apparently 


BASE  FROM  U.  S.  G.  S.  TOPOGRAPHIC  MAP 

(MARION   SHEET,    IOWA) 
91°  35' 


IOWA  GEOLOGICAL  SURVEY 
PLATE  II 


TOPOGRAPHIC  MAP  OF  A  PORTION  OF  THE  IOWAN 
DRIFT  PLAIN  IN  LINN  COUNTY,  IOWA 

Scale    62. "500 


Contour  Interval  20  feel 
Datum,  is  mean.  Sea,  leveL 


TOPOGRAPHY  OF  IOWAN  DRIFT  PLAIN  67 

generalized  contours  used.  The  contour  lines  which  mark  the 
reentrants  of  the  long  undissected  slopes  of  the  swales  should 
be  open,  rounded  curves,  such  as  are  shown,  rather  than  the 
sharply  angular  V-shaped  reentrants  required  to  represent  the 
dissected  slopes  of  the  Kansan  and  Illinoian  drift  areas. 

Comparison  of  Plate  II  with  Plate  I  shows  the  character  of 
the  lowan  drift  plain  as  here  represented  to  be  distinctly  dif- 
ferent from  the  much  dissected  topography  of  the  Kansan  drift. 
The  careful  and  critical  observer  who  has  seen  thousands  of 
square  miles  of  this  type  of  topography  is  impressed  with  the 
idea  that  it  must  be  the  result  of  some  different  geologic 
condition  from  that  which  produced  so  much  of  the  Kansan 
topography.  The  reader  should  bear  in  mind  that,  while  there 
are  limited  tracts  in  the  midst  of  the  lowan  area  and  especially 
in  the  border  belts  where  there  is  considerably  sharper  relief 
and  more  dissection,  the  type  here  shown  is  characteristic  of 
thousands  of  square  miles  of  the  lowan  drift  area.  It  is  the 
prevailing  type  of  the  lowan  drift  topography.  There  are  also 
some  limited  tracts  with  topography  similar  to  the  lowan  in 
the  Kansan  drift  area,  but  so  far  as  the  experience  of  the  writers 
goes  it  is  distinctly  the  exception  rather  than  the  rule  on  that 
drift. 

The  impression  gained  by  the  writers  from  a  careful  study 
of  this  topography  is  that  a  dendritic-branching  system  had 
developed  to  maturity  throughout  the  region  by  erosion,  but 
that  it  was  later  masked  in  the  lowan  drift  area  as  though 
overridden  by  an  ice  sheet  which  left  a  relatively  thin  mantle 
of  drift  thereon,  obliterating  the  minor  branches  of  the  drainage 
systems  but  leaving  the  main  valleys  and  major  branches  only 
partly  filled  and  that  the  amount  of  erosion  which  has  occurred 
since  the  disappearance  of  the  last  ice  sheet  has  been  relatively 
insignificant.  The  small  amount  of  this  erosion  as  compared 
with  that  in  the  Kansan  area  seems  to  the  writers  to  indicate 
that  the  time  since  the  disappearance  of  the  ice  from  the.  lowan 
drift  area  could  not  have  been  nearly  so  long  as  post-Kansan 
time.  They  therefore  regard  the  topographic  character  of  the 
lowan  area  as  a  whole  as  one  of  the  evidences  of  a  post-Kansa» 
glaciati'on  of  this  area. 


THE   IOWAN  DRIFT 


Fig. 


Unfortunately,  topographic  survey  of 
the  whole  area  of  the  lowan  drift  has 
not  been  made,  though  considerable  areas 
farther  north  than  that  shown  on  Plate 
II  are  shown  in  a  smaller  scale  (1:125000) 
on  the  Oelwein,  Elkader,  Winthrop,  and 
Farley  sheets.  Topography  of  this 
smooth-mantled  type  does  not  lend  itself 
well  to  illustration  by  photos  or  sketches 
because  of  the  lack  of  dissection  and  low 
angles  of  slope.  Certain  of  these  are,  how- 
ever, shown  in  Plates  V  and  VI,  where 
they,  are  contrasted  with  views  of  areas 
of  similar  maximum  topographic  relief  in 
the  Kansan  area.  These  views  are  not  ex- 
ceptional but  representative  in  character. 

Interpretation  of  the  lowan  topography, 
however,  requires  something  more  than 
mere  casual  inspection.  It  may  be  asked 
to  what  degree  this  mantled  appearance  of 
the  topography  in  the  lowan  drift  area  is 
lue  to  the  work  of  streams  having  been 
retarded  by  rock  cutting  as  compared  with 
the  streams  outside  this  area.  Study  by 
earlier  students,  by  members  of  the  Iowa 
Geological  Survey,  who  prepared  the  re- 
ports on  the  several  counties,  and  by  the 
present  writers  shows  that  there  has  been 
considerable  shifting  of  the  drainage  lines 
as  the  result  of  glaciation  of  the  area.  It 
is  not  now  known  how  much  of  this  was 
due  to  the  earliest,  or  Nebraskan,  ice  sheet, 
and  how  much  to  the  Kansan  glaciation. 
Records  of  wells  show  thicknesses  of  drift 
in  many  counties  to  vary  from  a  few  inches 
to  200  or  300  feet,  and  some  thicknesses  of 
nearly  400  feet  of  unconsolidated  deposits 
(mostly  drift)  are  reported.  In  some 
places  ancient  valleys  deeply  buried  have 
been  definitely  located.  One  of  these, 
which  may  for  convenience  be  referred  to 
as  the  ancient  valley  of  Wapsipinicon 
river,  is  shown  in  cross  profile  (figure  1). 

!• — Northeast-southwest  section  near  Anamosa  and  Monticello  showing  relations 
of  the  present  gorges  of  Wapsipinicon  and  Maquoketa  rivers  to  an  inter- 
vening, deeply  buried  river  valley. 


GORGE  CUTTING  IN  THE  IOWAN  AREA  71 

The  relations  in  the  case  of  this  stream  and  of  some  others 
seem  to  indicate  that  the  relocation  occurred  as  the  Kansan 
ice  sheet  melted  away,  leaving  former  valleys  blocked.  Post- 
Kansan  time  has  clearly  been  long,  for  the  streams  of  southern 
Iowa  have  accomplished  a  great  deal  of  dissection  of  that  area. 
In  many  places,  the  present  topography  of  the  Kansan  area  has 
been  carved  wholly  in  drift.  In  many  other  places,  however, 
the  streams  after  eroding  the  drift  have  cut  deeply  into,  and 
removed  large  amounts  of  the  older  rock. 

The  rock  underlying  the  Kansan  drift  area  is  largely  Car- 
boniferous shale  and  sandstone,  but  considerable  limestone  has 
also  been  encountered,  especially  in  the  lower  courses  of  the 
rivers.  In  the  lowan  area  the  drift  is  underlain  chiefly  by 
Silurian  and  Devonian  limestones.  The  shales  of  southern  Iowa 
may  perhaps  not  have  retarded  erosion  in  that  region  as  much 
as  did  the  limestones  in  northeastern  Iowa,  but  it  does  not  seem 
probable  that  the  greater  dissection  of  the  Kansan  drift  areas 
can  be  accounted  for  on  this  basis  alone.  In  the  belt  of  older 
drift  between  Mississippi  river  and  what  is  mapped  as  the 
approximate  east  boundary  of  the  lowan  drift,  Maquoketa, 
Wapsipinicon,  and  Cedar  rivers  have  cut  gorges  in  the  Niagaran 
limestone  in  Delaware,  Jones,  Jackson,  Cedar,  and  Johnson 
counties  apparently  in  post-Kansan  time.  The  depth  of  cutting 
in  rock  ranges  from  50  feet  or  less  to  about  125  feet.  These 
gorges  head  back  some  distance  into  the  lowan  drift  area. 
Closely  bordering  these  gorges  on  either  side  are  sharply  dis- 
sected tracts,  but  the  tributaries  are  in  general  short  and  the 
lateral  gorges  soon  head  at  rock  sills  in  the  lower  parts  of  the 
broad  open  swales.  This  latter  is  true  of  the  headwaters  of  the 
Volga,  Turkey,  and  Upper  Iowa  rivers  also.4  This  gorge-cutting 
must  have  had  a  considerable  retarding  effect  on  the  work  of 
the  streams,  but  even  so  it  is  doubtful  if  the  lack  of  dissection 
in  the  upper  stream  courses  in  the  lowan  drift  area  can  be 
accounted  for  by  this  retardation. 

*In  studying  the  sharply  dissected  topography  in  these  areas,  as  shown  on  the 
topographic  maps,  some  allowance  must  be  made  for  the  piling  up  on  hills  and 
sharpening  of  slopes  by  deposition  of  the  loess  subsequent  to  the  lowan  stage  of  glacia- 
tion  in  the  wooded  belts  bordering  these  streams.  It  is  not  so  much  a  case  of  the 
streams  leaving  the  interstream  plain  tracts  for  the  hills,  as  described  by  McGee,  as 
it  is  of  the  building  up  of  hills  of  eolian  deposits  bordering  the  streams  where  the 
brush  and  trees  so  retarded  the  winds  as  to  cause  deposition  of  the  dust  swept  off  the 
prairies.  • 


72  THE   IOWAN   DRIFT 

Owing  to  the  close  similarity  in  composition  of  the  lowan 
and  Kansan  drift  sheets,  as  shown  in  a  later  connection,  the  ap- 
proximate limits  of  the  lowan  glaciation  are  necessarily  largely 
determined  on  the  basis  of  topography.  The  boundary  has  in 
general  been  placed  where  the  smooth  swale  topography  on  the 
one  hand  gives  place  to  the  sharply  dissected  topography  on 
the  other.  In  the  study  in  the  field  it  was  found  that  the  eastern 
boundary  as  mapped  by  the  Iowa  Survey  in  any  given  valley, 
such  for  instance  as  that  crossing  Lime  creek  west  of  Hopkinton 
in  southern  Delaware  county,  had  been  placed  at  the  point  where 
the  stream  ceases  meandering  from  side  to  side  in  the  bottom 
of  a  broad  open  swale  and  begins  cutting  sharply  downward 
into  the  Niagaran  limestone.  Below  this  point  the  stream  flows 
in  a  constricted  gorge  whose  sides  are  picturesque  castellated 
cliffs  of  limestone,  in  places  nearly  100  feet  in  height.  The  con- 
trast is  very  striking  and  questions  at  once  arise  in  the  mind 
of  the  critical  observer,  "Do  the  broad,  open  swales  forming  the 
upper  parts  of  valleys  such  as  Lime  creek,  with  their  long, 
smooth  undissected  slopes,  represent  a  young  topography  due 
to  mantling  by  a  post-Kansan  drift  sheet,  or,  is  it  in  reality 
an  old  erosion  topography  in  an  area  which  has  been  rejuvenated 
and  where  the  newer  cycle  represented  by  the  gorge  cutting  has 
as  yet  advanced  only  so  far  up  stream  as  the  present  topography 
indicates  ? ' ' 

While  no  satisfactory  answer  to  this  question  was  found  on 
the  basis  of  topographic  configuration  alone,  there  are  several 
considerations  which  seem  to  the  writers  to  indicate  that  there 
has  really  been  mantling  of  a  maturely  eroded  topography  by  a 
post-Kansan  drift  sheet  in  the  area  mapped  as  lowan  drift. 

It  is  true  that  the  gorge-cutting  represents  a  new  cycle  of 
erosion  (post-Kansan  probably)  in  each  such  valley  and  the 
gorge-cutting  has  progressed  only  to  a  point  where  the  stream 
is  now  on  rock  in  the  bottom  of  the  swale.  If,  however,  the  swale 
is  simply  a  mature  topography  developed  on  the  Kansan  drift 
by  erosion  alone  and  not  mantled  by  a  later  drift,  the  long,  low 
slopes  would  seem  to  represent  an  older  stage  of  erosion  than 
that  reached  lower  down  in  the  valley.  On  this  basis,  consider- 
ing the  lowan  area  as  a  whole  as  compared  with  the  Kansan 


GORGE  CUTTING  IN  THE  IOWAN  AREA  73 

area  to  the  south,  we  would  be  led  to  conclude  that  the  heads 
of  the  tributaries  of  the  upper  Mississippi  basin  had  reached 
a  more  advanced  stage  of  erosion  than  the  tributaries  of  the 
same  system  farther  south.    This  is  in  itself  improbable.    One 
might  suppose  that  the  rock  exposed  in  the  lower  parts  of  the 
swales  retarded  dissection  in  the  upper  parts,  yet  the  angles 
of  the  side  slopes  range  from  2°  to  8°,  quite  adequate  for  dissec- 
tion if  the  valleys  are  old  enough.    In  fact,  it  is  surprising  that 
they  have  not  been  cut  by  ravines   since  the  lowan  ice  dis- 
appeared.   This  may,  indeed,  afford  ground  for  an  opinion  that 
some  unknown  factors  are  involved.     One  might  also  suppose 
that  the  drift,  being  more  readily  eroded  than  the  limestone, 
would  permit  a  mature  stage  of  erosion  to  be  reached  in  the 
drift  of  the  upper  part  of  the  valley  while  the  stream  was  yet 
cutting  the  constricted  gorge  in  limestone  in  the  lower  part. 
It  is  to  be  noted,  however,  that  the  same  relations  of  drift  and 
limestone  occur  in  the  Kansan  area  to  the  south,  yet  there  is, 
in  general,  so  far  as  the  writers  have  seen,  no  such  combination 
of  broad  swales  and  low  slopes  on  the  upper  stream  reaches 
with   sharp   gorge-cutting  lower  down.     As   shown  in  Plates 
V,  B  and  VI,  B  and  as  described  above,  the  heads  of  the  streams 
in  the  Kansan  area  are  minutely-branching,   sharply-cut,   V-- 
shaped ravines  scoring  the  slopes  at  frequent  intervals.     The 
smooth  swale  topography  so  prevalent  in  the  lowan  area  seems 
to  the  writers  to  correspond  very  closely  to  what  one  would 
expect  if  a  maturely  dissected  area  were  overridden  by  a  re- 
advance  of  the  ice  and  left  mantled  with  a  drift  sheet  of  mod- 
erate thickness.     Besides  the  definite  evidence  of  the  presence 
of  a  post-Kansan  drift  sheet  it  is  shown  in  a  later  connection 
that,   subsequent  to  the   cutting  of  the  gorges,  gravels  were 
washed  into  and  through  them  and  deposited.     These  gravels, 
which  may  be  regarded  as  outwash  from  the  lowan  ice  sheet, 
have  since  been  largely  removed  by  erosion  so  that  in  places 
only  remnants  are  found  as  terraces  bordering  the  streams. 
The  topographic  condition  of  the  lowan  area  taken  in  connec- 
tion with  the  direct  evidence,  presented  later,  of  the  presence  of 
a  thin  drift  sheet  apparently  of  post-Kansan  age  and  of  out- 
wash  gravels  to  be  correlated  therewith,  seems  to  the  writers 


74  THE   IOWAN   DRIFT 

to  make  the  case  for  the  lowan  stage  of  glaciation  fairly  strong. 
The  only  other  alternative  seems  to  be  that  in  their  study  of 
the  topography  some  very  important  factor  has  been  wholly  left 
out  of  the  consideration.  It  is  not  clear,  however,  that  this  is 
the  case. 

The  occurrence  of  broad  interstream  areas  which  seem  to 
have  been  covered  by  the  lowan  ice  sheet  between  the  dissected 
belts  bordering  parts  of  Maquoketa,  Wapsipinicon,  and  Cedar 
rivers  leads  to  the  inference  that  the  lowan  ice  really  extended 
into  the  gorges,  but  that  the  ready  avenues  of  escape  for  the 
glacial  water  resulted  in  most  of  the  somewhat  meager  drift 
being  swept  down  the  valleys  by  the  streams  and  in  such  as 
remained  being  left  mostly  as  waterlaid  sand  and  gravel.  The 
lobate  margin  of  the  lowan  drift  as  mapped  by  Doctor  Calvin 
and  his  associates  gives  to  the  reader  the  impression  that  the 
margin  of  the  ice  was  actually  similarly  lobate  at  its  maximum 
extension.  It  seems  impossible,  however,  to  think  that  the  ice- 
occupied  the  interstream  uplands  and  did  not  extend  down  into 
the  valleys  which  were  in  reality  considerably  lower,  especially 
before  the  bordering  loess  hills  were  deposited.  The  writers 
have  not  made  careful  and  detailed  search  of  these  valleys  for 
remnants  of  the  lowan  drift,  but  it  seems  necessary  to  conclude 
that  the  ice  really  lay  in  these  valleys  and  thus  a  generalized 
boundary  of  the  area  covered  by  the  lowan  ice  sheet  if  it  in- 
cludes most  of  the  lobate  drift  tracts  which  have  been  mapped, 
should  extend  across  the  intervening  valleys  with  their  dissected 
border  belts.  This  is  discussed  in  a  subsequent  connection 
(see  Chapter  VIII). 

While  the  prevalent  topographic  character  of  the  lowan  drift 
area  is  such  as  appears  to  have  resulted  from  the  mantling  of 
a  maturely  developed,  post-Kansan,  erosional  topography,  there 
are  exceptional  areas  where  there  is  considerable  sharp  dissec- 
tion and  where  the  topography  appears  not  to  have  been 
mantled.  Keference  has  already  been  made  to  the  principal 
areas  of  this  kind  along  Maquoketa,  Wapsipinicon,  Cedar,  and 
Iowa  rivers.  There  is  an  isolated  tract  of  this  sort  on  the 
Maquoketa  in  the  northwestern  part  of  Delaware  county,  north 
of  Dundee.  The  stream  here  flows  through  a  picturesque  'wind 


UPPERMOST  TILL  OF  THE  IOWAN  AREA  77 

ing  gorge  50  to  150  feet  in  depth  cut  in  the  Niagaran  limestone. 
On  the  melting  of  the  ice  sheet  the  stream  was  superimposed  on 
a  buried  ridge  of  limestone.  The  subsequent  work  of  the  stream 
has  developed  the  gorge.  If  the  shifting  was  the  work  of  the 
Kansan  ice  it  seems  necessary  to  suppose  that  the  lowan  ice 
filled  the  gorge,  but  did  not  leave  it  buried  in  drift.  On  the  other 
hand,  it  may  be  the  gorge  is  of  post-Iowan  age,  but  this  seems 
doubtful.  A  similar  rock  gorge  is  traversed  by  Cedar  river  at 
and  above  Osage. 

Some  loess-covered  hilly  tracts  have  been  shown  on  the  maps 
of  the  Iowa  Survey  as  loess-covered  Kansan  drift.  None  of 
these  areas  is  so  high  that  it  can  be  supposed  that  the  lowan 
ice  did  not  cover  it.  It  is  hardly  possible  to  conceive  of  an  ice 
sheet  competent  to  extend  150  miles  or  more  southeastward  in 
Iowa  and  to  spread  over  an  area  of  9,000  square  miles  which 
was  so  thin  as  not  to  cover  hills  100  feet  or  less  in  height.  Oit 
the  other  hand,  the  load  of  drift  carried  by  this  ice  was  probably 
not  very  great  and  though  covered  by  ice  the  hills  may  well  have 
been  unmantled  or  thinly  mantled  with  lowan  drift,  as  was 
clearly  the  case  in  some  other  places.  The  steep  slopes  of  these 
hilly  tracts  would  favor  erosion  and  the  subsequent  removal  of 
thin  drift.  Moreover,  their  mantle  of  loess  does  not  everywhere 
permit  a  determination  of  just  what  drift  is  present.  Such 
tracts  occur  in  Mitchell,  Butler,  Bremer,  Black  Hawk,  Benton, 
and  Linn  counties.  An  exposure  on  one  such  hilly  tract  south- 
east of  Hampton  showed  two  feet  of  till,  presumably  lowan, 
overlying  much  weathered  drift  or  " gumbo,"  probably  Kansan. 


CHAPTER  II 

THE  UPPERMOST  TILL  OF  THE  IOWAN  AREA, 

If  the  topographic  configuration  of  the  lowan  drift  area  is 
the  result  of  post-Kansan  glaciation  and  the  deposition  of  a 
mantle  of  till  on  the  dissected  surface  of  the  Kansan,  it  is  to 
be  expected  that  the  uppermost  drift  of  the  lowan  area  would 
show  less  modification  by  weathering  than  that  of  the  parts  of 
the  Kansan  drift  area  immediately  adjacent.  Conversely,  if  the 


78  THE   IOWAN   DRIFT 

drift  generally  exposed  at  the  surface  throughout  the  lowan 
area  shows  on  the  whole  less  modification  by  weathering  than 
does  that  of  the  Kansan  area,  it  may  be  regarded  as  one  evi- 
dence of  post-Kansan  glaciation  of  the  area. 

It  may  be  contended  that,  unless  the  Iowa  drift  has  distinctive 
lithologic  or  other  characters  by  which  it  can  be  identified  in 
every  exposure  (and  unfortunately  it  has  not),  or  unless  it  is 
everywhere  distinctly  separated  from  the  underlying  drift  by  a 
soil  or  weathered  zone  (which,  of  course,  is  not  the  case  with 
any  drift  sheet),  it  is  not  permissible  to  infer  that  the  upper- 
most drift  at  all,  or  even  most,  places  in  the  area  is  the  latest, 
drift  of  the  area.  Thus  any  generalized  statement  of  the  char- 
acter of  the  uppermost  drift  of  the  lowan  area  might  be  said 
to  be  merely  a  description  of  the  upper  part  of  the  Kansan  drift, 
which  is  believed  to  be  the  main  drift  sheet  in  northeastern 
Iowa,  or  be  a  combination  of  data  from  exposures,  some  of  them 
in  lowan  drift  and  some  of  them  in  Kansan,  and  so  not  be  really 
representative. 

One  familiar  with  the  usual  conditions  of  exposure  of  glacial 
deposits  and  knowing  how  far  short  of  what  are  theoretically 
desirable  for  the  proper  discrimination  of  different  drift  sheets 
are  these  conditions  must  admit  the  justice  of  such  statements. 
These  limitations  apply,  however,  in  all  drift  areas  and  are  not 
confined  to  the  lowan  drift  area.  There  are  places  in  the  lowan 
area  where  the  total  of  all  drift  deposits  remaining  is  very 
small,  in  spots  nothing  at  all,  yet  the  writers  are  quite  firmly 
of  the  opinion  that  an  ice  sheet  of  sufficient  volume  to  spread 
so  far  south  and  cover  9,000  square  miles  in  northeastern  Iowa 
could  not  have  failed  to  transport  a  considerable  amount  of 
drift  and  to  have  left  a  till  sheet  which  was  composed  of  more 
than  patches  of  material  derived  from  the  deeply  weathered 
upper  part  of  the  Kansan  drift.  There  should  be  a  till  sheet 
of  at  least  moderate  thickness  spread  generally  over  the  area 
though  perhaps  locally  very  thin  or  even  absent  in  spots.  If 
the  topographic  configuration  is  due  to  mantling  of  a  dissected 
Kansan  topography,  as  the  writers  believe  it  to  be,  there  must 
have  been  enough  glacial  abrasion  and  deposition  of  drift  to 
produce  the  mantling.  It  is,  therefore,  fair  to  expect,  if  a  large 


LITHOLOGY  OF  THE  IOWAN  DRIFT  79 

number  of  exposures  are  examined  and  if  a  large  number  of 
borings  are  made,  well  distributed  over  the  smoothly  mantled 
area,  that  a  compilation  of  the  data  will  give  a  fairly  good  idea 
of  the  general  character  of  the  latest  drift  of  the  area,  and  of 
the  amount  of  its  modification  by  weathering. 

Scores  of  exposures  throughout  the  lowan  drift  area  were 
studied,  and  the  constitution,  physical  features,  and  degree  of 
modification  of  the  till  by  weathering  were  noted.  The  recent 
improvement  of  wagon  roads,  construction  of  interurban  elec- 
tric railway  lines  and  the  regrading  of  the  Chicago,  Milwaukee 
and  St.  Paul  railway  have  afforded  many  new  exposures.  The 
majority  of  the  cuts  in  this  area  are  less  than  fifteen  feet  deepr 
and  few  are  so  much  as  twenty  feet.  On  account  of  the  small 
amount  of  dissection  of  the  lowan  area,  there  are  localities 
where  road  cuts  or  excavations  of  any  kind  are  few.  In  such 
areas  a  two-inch  auger  eight  feet  in  length  was  used  for  making 
test  borings. 

The  following  is  a  generalized  section  of  the  deposits  shown 
by  these  exposures : 

GENERALIZED  SECTION. 

Feet 

4.  Soil,  black  to  dirty  brown,  usually  pebblelesss  or 
pebbles  rare;  where  thicker  than  two  feet  the  lower 
part  is  yellow  and  looks  like  loess,  thickness 1  to  2^4 

3.    Pebble-line   (in  some  cuts) 

2.  Leached  till,  light  brownish  yellow  to  buff,  clayey 
matrix;  pebbles  of  granite,  greenstone,  and  chert — and 
some  of  felsite,  basalt,  dolerite,  volcanic  porphyry, 
quartzite,  and  vitreous  quartz;  some  of  the  granite 
sound,  some  disintegrated;  greenstone  mostly  fresh; 
absence  of  limestone  pebbles  and  noncalcareous  con- 
stituents conspicuous;  thickness  3  to  5 

Grades  rather  abruptly  into: 

1.  Calcareous  till,  limestone  pebbles  present  together  with  the 
other  varieties  found  in  the  leached  zone,  color  changes  by 
gradation  downward  from  buff  to  gray  or  slate-color  eight  to 
ten  feet  from  top  of  till-body. 

The  Lithology  of  the  lowan  Drift  and  Its  Comparison  With  Other 

Drifts. 

Rough  determinations  of  lithologic  composition  were  made  by 
collecting  and  sorting  pebbles  from  numerous  exposures  of  each 
of  the  following  drift  sheets  in  Iowa,  the  Nebraskan,  Kansan, 
lowan,  and  Wisconsin  drifts.  The  results  of  these,  together 
with  numerous  similar  estimates  made  by  R.  T.  Chambering 


go  THE   IOWAN  DRIFT 

in  1907,  are  presented  in  tables  in  Appendix  A  for  ready 
comparison.  From  Table  2  it  will  be  seen  that  the  pebbles  of 
the  unleached  lowan  drift  comprise  mainly  granites,  greenT 
stones,  limestones,  schists,  quartzites,  quartz,  cherts  and  sand- 
stone. It  will  be  noted  that  the  percentage  of  each  constituent 
varies  considerably  from  place  to  place,  and  that  the  general 
composition  of  this  drift  is  not  distinctive.  This  being  the  case, 
unless  the  two  drifts  are  exposed  in  the  same  section  with  a 
weathered  zone  or  interglacial  deposits  clearly  marked  between, 
one  cannot  always  be  sure  that  any  particular  section  is  in  lowan 
till  and  not  Kansan.  The  only  lithologic  distinction  which  the 
lowan  drift  sheet  possesses  seems  to  be  the  greater  abundance 
of  large  granite  bowlders  in  the  eastern  and  central  parts  of 
the  area.  These  bowlders  are  considered  in  Chapter  V. 

In  general,  however,  it  may  be  stated  that  the  limestone  con- 
tent of  the  Wisconsin  drift  is  higher  than  that  of  any  other 
(See  Table  I) ;  that  the  formation  of  ironstone  concretions  in 
the  altered  zone  and  the  concentration  of  calcium  carbonate  in 
the  unleached  zone  of  the  lowan  drift  are  less  notable  than  is 
the  case  with  the  Kansan  drift.5  The  latter  point  suggests  that 
the  Kansan  drift  has  undergone  more  prolonged  weathering 
than  the  lowan. 

THE  OXIDATION  OF  THE  TILL. 

In  most  places  oxidation  to  a  buff  or  bright  yellow  tint  has 
extended  to  depths  below  the  reach  of  the  eight-foot  auger. 
Yet  in  many  places  bluish  gray  unoxidized  till  was  reached  in 
boring.  As  seen  in  cuts,  oxidation  was  found,  in  most  places, 
to  have  changed  the  original  bluish  gray  or  drab-gray  color  of 
the  till  to  light  buff  to  depths  somewhat  greater  than  the  leach- 
ing had  extended,  that  is,  usually  to  depths  of  seven  to  ten  feet. 
Below  these  depths  the  color  gradually  changes.  The  color  in 
the  oxidized  part  of  the  till  generally  ranges  from  light  buff  at 
the  bottom  to  brown  at  the  top.  In  many  places,  as  in  Bremer 
county,  the  upper  part  below  the  soil  is  a  bright  ocher-yellow, 
but  rarely  is  it  orange  and  seldom  is  there  a  distinct  reddish 
tint  as  in  the  Kansan  ferretto.  In  some  places  the  bluish  gray 

6It  should  be  noted  that  the  true  percentages  of  clay  ironstones  and  calcareous  con- 
cretions are  riot  frpieraliir  Pv,own  in  thf>  tables  o^  estimates  since  in  collecting  pebbles, 
the  writers  aimed  to  avoid  these  secondary  constituents. 


EFFECTS  OF  LEACHING  81 

till  is  considerably  more  dense  and  hard  than  the  oxidized  and 
leached  till  and  grades  below  into  dense,  hard,  dark,  slate- 
colored  till.  In  these  instances  the  unoxidized  till,  at  least,  is 
probably  Kansan. 

If  the  interglacial  deposits  or  the  red  ferretto  characteristic 
of  the  top  of  the  Kansan  have  been  removed  by  erosion  and  a 
deposit  of  lowan  till  left  instead  a  given  cut  may  show  buff 
lowan  till  over  buff  Kansan  till  with  no  apparent  break  between. 
This  is  one  of  the  factors  that  makes  the  determination  of  the 
exact  limits  of  the  lowan  drift  well-nigh  impossible.  It  cer- 
tainly is  not  safe  to  regard  all  the  buff  or  yellow  till  as  lowan 
and  only  the  blue-gray  or  blue-black  unoxidized  part  as  Kansan, 
as  seems  to  have  been  done  in  some  cases. 

Fortunately,  however,  as  described  on  page  92  there  are  a 
number  of  places  where  the  weathered  zone  and  interglacial  soil 
at  the  top  of  what  is  regarded  as  Kansan  drift  are  well  pre- 
served/with  an  overlying  deposit  of  till,  presumably  lowan. 

THE  EFFECTS  OF  LEACHING. 

Examination  was  made  of  sixty-five  exposures  which  showed 
the  change  from  calcareous  to  leached  till.  The  clayey  matrix 
was  tested  with  cold  dilute  hydrochloric  acid.  The  limestone 
pebbles  were  present  in  the  former  but  mostly  absent  from  the 
latter.  As  shown  in  Table  3,  Appendix  A,  seven  estimates  where 
the  pebbles  were  taken  only  from  the  leached  upper  part  of  the 
drift  show  an  average  of  but  three  per  cent  of  limestone  and 
dolomite,  while  the  percentages  of  the  relatively  insoluble  con- 
stituents were  correspondingly  higher. 

Besides  examining  the  exposures,  250  auger  borings  were 
made,  where  cuts  were  not  available,  to  ascertain  the  depth  of 
the  leached  zone  and  character  of  the  till.  One  hundred  and 
sixty-five'  of  these  were  in  the  interior  of  the  area  and  eighty- 
five  nearer  the  border. 

Following  is  a  tabulation  of  the  results  obtained  by  examining 
the  exposures  and  making  auger  borings: 


81' 


THE   IOWAN  DRIFT 


DEPTH  OF  LEACHING  |     NUMBER  OF 
FEOM  TOP  OF  TILL  |         CUTS 


NUMBEB  OF 
BOEINGS 


iTEBCENTAGE   OF  |  FEBCENT  AGE    OF 

CUTS          I      BOEINGS 


0-1 

1 

1     |      2 

1 

1-1% 

3 

12    V      5 

7 

2-2% 

7 

25 

12 

15 

3-3% 

24 

55 

42 

33 

4-4% 

12 

37 

21 

23 

5-5%           9 

18 

15 

11 

6-6% 

2 

13 

2 

8 

7-8 

1 

4 

1 

2 

Total 


10 


20 


30 


40 


50 


FEET 
0-1 

I-I/Z 
3-3/2 

5-5/2 
6-6/2 
7-8 


t-f 

Fig.  2. — Diagram  of  percentages  of  cuts  and  borings  showing  different  depth 
leaching  of  the  uppermost  till  at  various  places  in  the  area  of  the  lo 
drift. 


of 
iwan 


The  curve  in  figure  2  represents  graphically  the  foregoing 
results. 

This  compilation  shows  that  the  larger  number  of  cuts  and 
borings  give  a  depth  of  leaching  of  three  to  three  and  one-half 
feet;  that  seventy-eight  per  cent  of  the  cuts  and  sixty-seven 
per  cent  of  the  borings  indicate  a  range  of  depth  from  three  to 
five  and  one-half  feet;  and  that  only  one  per  cent  of  the  cuts 
and  two  per  cent  of  the  borings  showed  as  much  as  eight  feet 
of  leaching. 

In  the  border  belt  the  depth  of  leaching  is  less  uniform  and 
averages  somewhat  more.  Fifty-four  per  cent  of  the  borings 
showed  the  depth  of  leaching  as  four  to  six  and  one-half  feet, 
thirty- two  per  cent  less  than  four  feet,  and  fourteen  per  cent 
as.  much  as  seven  and  one-half  feet. 


COMPARISON  WITH  THE  KANSAN  TILL  83 

The  overlying'  loesslike.  clay. — Generally  soil  and  loesslike  clay 
one  to  two  and  one-half  feet  thick  overlie  the  till  of  the  lowan 
area.  This  deposit  is  not  included  in  the  measurements  of 
leached  till.  It  appears  to  be  a  thin  mantle  of  loess  which  has 
largely  lost  some  of  its  typical  character  as  the  result  of  leach- 
ing, freezing  and  thawing,  burrowing  of  animals,  the  influence 
of  vegetation  and  mixing  with  humus  in  the  upper  foot  or  so. 
Where  the  deposit  is  more  than  two  and  one-half  feet  thick,  its 
lower  part  is  identical  in  character  with  loess.  As  seen  in  cuts 
it  is  generally  separated  from  the  till  by  a*  distinct  line  of 
pebbles,  which  are  probably  the  residue  from  wash  and  wind- 
erosion  of  the  upper  part  of  the  till. 

If  this  thin  coating  of  loess  was  deposited  as  calcareous 
material  immediately  after  the  deposition  of  the  till,  its  thick- 
ness should  be  included  in  the  depth  of  leaching  which  has  taken 
place  since  the  till  was  deposited.  If  it  was  added  later  as  non- 
calcareous  material  derived  from  the  weathered  surface  of  the 
till,  then  its  effect  on  the  leaching  of  the  underlying  till  has  been 
slight.  A  part  of  it  may  have  had  the  former  history,  a  part  of 
it  the  latter. 

COMPARISON  WITH  THE  KANSAN  TILL. 

The  oxidation  of  the  Ka/nsan  drift. — The  uppermost  till  of 
the  unquestioned  Kansan  area  was  studied  in  railroad  sections 
and  road  cuts  to  the  south  and  east  of  the  lowan  drift  area.  Its 
oxidation,  decomposition,  and  leaching  were  carefully  noted. 
The  change  in  the  Kansan  drift  as  the  result  of  oxidation  differs 
from  that  of  the  uppermost  drift  of  the  lowan  area  in  two 
particulars, — in  degree  and  in  depth.  In  most  of  the  places  seen 
the  Kansan  drift  is  overlain  by  loess.  The  prevalence  of  a 
reddish  brown  or  dark  brown  ferretto  zone  at  the  top  of  the 
till  and  beneath  the  loess  is  a  conspicuous  phenomenon.  This 
ferretto,  which  averages  one  to  one  and  one-half  feet  thick, 
consists  of  a  dense,  sticky  clay  containing  many  decomposed 
granites,  greenstones,  and  other  igneous  rocks,  together  with 
quartzites,  quartz,  cherts,  and  clay  ironstones.  It  grades  down- 
ward into  brownish  and  yellowish  leached  till.  The  material 
has  the  appearance  of  being  the  relatively  insoluble  residuum  of 
prolonged  leaching,  oxidation,  decomposition,  and  dehydration 


84  THE  IOWAN  DRIFT 

of  a  somewhat  greater  thickness  of  the  upper  part  of  the  till. 
Its  advanced  state  of  decay  matches  its  setting  in  the  much 
eroded  Kansan  area.  In  many  exposures  the  ferretto  is  cut  off 
well  up  in  the  eroded  slope  as  though  it  had  been  formed  before 
the  present  stage  of  dissection  was  reached. 

The  ferretto  band  is  fairly  persistent  in  the  crests  of  the 
ridges  throughout  those  dissected  parts  of  the  Kansan  drift 
area  which  were  visited  by  the  writers,  and  it  is  strongly  in 
contrast  with  the  brownish  yellow  color  of  the  upper  part  of 
the  drift  in  the  lowan  area.  The  ferretto  was  seen  within  the 
boundaries  of  the  lowan  area,  in  three  or  four  places  only. 
At  one  or  two  of  these  there  was  evidence  of  mechanical  mixing 
with  fresher  till,  as  if  the  ferretto  had  been  disturbed  by  an 
overriding  ice-sheet.  The  other  cases  were  in  isolated  localities 
of  sharp,  mature  erosion,  where  the  topography  lacks  the 
mantled  aspect. 

Not  only  is  there  a  significant  difference  between  the  degree 
of  oxidation  of  the  uppermost  till  in  the  lowan  area  and  that 
of  adjacent  parts  of  the  Kansan  areas,  but  also  in  the  depth  of 
oxidation.  The  Kansan  drift  is  oxidized  to  depths  of  fifteen 
to  twenty-five  feet  below  the  base  of  the  loess,  as  compared 
with  eight  to  ten  feet  for  the  lowan  drift. 

While  the  writers  regard  this  sort  of  evidence  as  entirely 
legitimate,  they  do  not  think  these  measurements,  those  given 
above,  or  those  following,  can  be  applied  indiscriminately  in 
other  areas.  The  similarity  in  climate  at  present  between  north- 
eastern Iowa  and  adjacent  parts  of  southern  Iowa  and  Illinois 
seems  to  warrant  direct  comparisons  of  the  amount  of  modifica- 
tion by  weathering  of  the  several  drift  sheets.  Going  to  another 
region,  however,  as,  for  example,  to  the  drier  climates  farther 
northwest,  the  same  differences  may  not  be  found.  If  contrasts 
in  degree  and  in  depth  of  oxidation  of  deposits  in  two  areas, 
lying  side  by  side,  are  to  be  regarded  as  at  all  indicative  of 
difference  in  age,  the  data  cited  are  certainly  significant.  The 
strong  oxidation  is  found  where  there  is  the  deeply  dissected 
topography  of  the  Kansan,  the  moderate  oxidation  is  associated 
with  the  mantled  and  little  eroded  topography  of  the  lowan 
area.  This  evidence  seems  to  support  the  conclusion  of  differ- 
ence in  age  reached  from  the  study  of  the  topography. 


LEACHING  OF  THE  KANSAN  DRIFT  85 

The  leaching  of  the  Kcmsan  drift.  —  If  mature  erosion,  the 
presence  of  a  ferretto,  and  greater  depth  of  oxidation  dis- 
tinguish the  drift  of  the  Kansan  area  from  that  of  the  lowan 
area  and  indicate  a  greater  age  for  the  former,  the  leaching  of 
the  Kansan  till  should  at  least  be  consistent  with  this  view. 

In  critically  examining  data  bearing  on  the  leaching  of  the 
Kansan  till,  attention  to  the  topographic  position  of  the  expo- 
sure is  important.  In  a  sharply  dissected  topography,  the 
leaching  of  the  till  on  the  lower  slopes  must  date  from  the  time 
that  the  drift  in  that  topographic  position  was  brought  within 
the  zone  of  lefjching  by  the  removal  of  the  overlying  material, 
i.  e.,  from  a  time  when  most  of  the  erosion  had  been  accom- 
plished. The  diagram  (figure  3)  of  a  specific  case  illustrates 

Upland 


Probable   original   surface 


R! 


Fig.   3.  —  Diagram    of    valley    slope    in    Kansan    drift    area    four    miles    northeast    of 
Victor    (Iowa  County,    Hartford    township;    Township   80    North,    Range    12 
west,  east  line  southeast  quarter  section  3.     a.     Position  of  road  cut  showing 
till  leached  to  depth  of  five  feet. 

a  prevalent  condition.  A  road  cut  at  a  shows  a  leached  zone 
of  five  feet.  Obviously,  this  thickness  may  have  been  added  to 
by  deposition  or  subtracted  from  by  slope-wash.  But  if  we 
assume  that  the  thickness  is  a  true  record  of  the  depth  of  leach- 
ing in  place,  it  still  can  not  be  taken  as  indicative  of  the  full  age 
of  the  drift  but  rather  as  a  measure  of  the  time  since  that  par- 
ticular portion  of  the  drift  was  subjected  to  leaching. 

One  must  discriminate  also  in  interpreting  the  data  collected 
from  railroad  cuts,  similarly  located.  To  illustrate  again,  refer- 
ence may  be  made  to  a  Chicago,  Milwaukee  and  St.  Paul  railway 
cut  in  a  locality  of  sharp  dissection  in  Tama  county,  west  of 
Vining,  Otter  Creek  township,  southwest  quarter  of  section  13. 
The  cut  is  150  yards  long,  has  a  maximum  depth  of  25  feet,  and 
transects  the  lower  parts  of  two  long  spurs.  In  vertical  section 
the  relations  are  as  follows  (figure  4). 

At  a  a  ferretto  and  a  leached  zone  of  till  four  or  five  feet  thick 
lies  beneath  calcareous  loess.  At  b  and  b1  these  are  absent  and 


86  THE  IOWAN  DRIFT 


Ferretto  and 
leached  buff  til 
4-5  feet 


-gray  ti 

Fig  4 — Diagram  of  drift  exposed  in  Chicago,  Milwaukee  &  S't.  Paul  Railway  cut 
three  miles  west  of  Vining,  Tama  County,  Iowa,  showing  relation  of  loess 
to  weathered  and  unweathered  Kansan  drift.  Length  450  feet.  Height 
25  feet. 

the  calcareous  loess  rests  directly  on  calcareous  till  containing 
limestone  pebbles.  The  relations  at  a  record  an  interval  of  leach- 
ing and  oxidation  between  the  development  of  the  surface  of  the 
till  at  this  horizon  and  the  deposition  of  the  overlying  loess.  This 
record,  however,  covers  only  a  fraction  of  the  interval  between 
the  deposition  of  the  till  and  the  deposition  of  the  loess.  It  lacks 
at  least  the  time  consumed  in  the  erosion  of  the  original  drift 
plain  down  to  this  horizon.  Furthermore,  the  difference  in  re- 
lations at  a  and  b  are  suggestive  of  the  unreliable  character  of 
the  data  even  for  the  interval  between  the  slope  development  and 
the  deposition  of  the  loess.  If  the  relations  at  fe1  only  were 
known,  there  would  be  absolutely  no  record  of  the  interval  of 
leaching.  Obviously,  erosion,  or  slope-wash,  at  b  and  &1  overtook 
and  surpassed  the  rate  of  leaching  so  that  the  weathered  zone 
was  removed  before  the  loess  was  deposited. 

It  is  evident  from  such  conditions  that  the  depths  of  leaching 
ascertained  from  exposures  on  slopes  may  be  much  less  than  the 
actual  total  amount  of  leaching  of  the  Kansan  till.  Better  places 
for  such  measurements  would  probably  be  in  cuts  through  the 
upland  divides,  but  such  are  few. 

A  cut  forty-five  feet  deep,  about  three-fourths  mile  east  of  Vin- 
ing, situated  almost  half  way  up  the  slope  of  a  spur,  shows  as 
much  as  seven  feet  of  leaching  at  the  top  of  the  till  below  cal- 
careous loess,  which  in  turn  is  overlain  by  leached  loess.  But 
even  here  the  top  of  the  till  is  considerably  below  the  general  up- 
land level  and  its  surface  is  rounded. 

West  of  Melbourne,  Marshall  county,  there  are  three  cuts 
within  four  miles,  similarly  situated  topographically,  which  show 
a  like  depth  of  leaching,  and  four  others  higher  up  on  the  slopes 
of  spurs,  which  show  leaching  to  depths  of  twelve,  thirteen, 
twelve  and  eleven  feet,  respectively.  In  all  of  these  cuts  the 
leaching  took  place  before  the  loess  was  deposited. 


LEACHING  OP  THE  KANSAN  DRIFT  87 

Two  and  one-half  miles  west  of  Rhodes,  Marshall  county,  at 
the  edge  of  the  Wisconsin  drift  sheet,  in  a  cut  seventy  feet 
deep,  ten  feet  of  nonoalcareous  gumbo  and  ten  feet  of  leached 
Kansan  till  overlie  calcareous  Kansan  till  and  underlie  loess  and 
Wisconsin  drift.  If  the  gumbo  is  the  product  of  weathering  of  the 
Kansan  till,  as  is  believed  by  some  recent  workers,  the  leached 
zone  in  this  case  would  be  at  least  twenty  feet. 

If  the  gumbo  is  really  the  concentration  of  the  least  readily 
soluble  constituents  of  the  upper  part  of  the  till,  i.  e.,  the  resid- 
uum of  long  leaching,  each  foot  of  its  thickness  represents  more 
than  one  foot  of  the  original  till  before  the  soluble  parts  were  re- 
moved. Whether  or  not  the  gumbo  is  such,  it  seems  clear  that 
the  ferretto  zone  is  the  result  of  such  concentration,  together 
with  oxidation,  and  represents  a  somewhat  greater  thickness  of 
unleached  till. 

It  appears  that  some  appreciable  part  of  the  till  is  composed 
of  the  soluble  part  of  the  limestone  pebbles,  since  these  comprise 
nearly  fifty  per  cent  of  all  the  pebbles  in  the  drift  and  with  these 
goes  the  calcareous  rock  flour  in  the  matrix  of  the  till.  If  accurate 
determinations  were  being  made  of  the  total  depths  of  leaching, 
some  small  amount  should  be  added  to  the  present  thicknesses  of 
the  leached  zone.  In  the  rough  determinations  made  in  this  in- 
vestigation, however,  this  factor  may  be  omitted. 

Comparing  then  the  leached  zone  of  the  Kansan  drift  near  the 
original  upland  in  adjacent  areas  with  the  leached  zone  in  the 
lowan  drift  area,  depths  of  eleven  to  thirteen  feet  in  the  former 
as  compared  with  three  to  five  and  one-half  feet  in  the  latter 
emphasize  the  greater  age  of  the  Kansan  drift  over  that  of  the 
lowan. 

But  yet  the  whole  difference  has  not  been  pointed  out.  The  rate 
of  leaching  undoubtedly  decreases  with  depth,  due  to  (1)  the  less 
amount  of  percolating  water  on  account  of  capillary  action 
bringing  a  part  back  to  the  surf  ace;  (2)  the  slower  movement  of 
the  ground  water  with  increased  compactness,  and  (3)  the  de- 
creased solvent  action  of  the  water  as  the  result  of  the  dissolving 
of  some  materials  during  descent.  Hence,  the  relative  length  of 
time  is  probably  something  more  than  the  ratio  of  the  foregoing- 
figures. 


88  THE  IOWAN   DRIFT 

Another  point  of  importance  remains  to  be  noted.  The  leached 
zone  of  the  Kansan  drift  lies  beneath  calcareous  loess,  which  in 
turn  is  overlain  by  leached  loess  five  to  ten  feet  thick.  This 
stratigraphic  relation  shows  that  the  period  of  leaching  of  the 
Kansan  drift  is  separated  from  the  present  by  an  interval  of 
loess  deposition  and  of  subsequent  leaching  of  the  loess  to  depths 
varying  from  five  to  ten  feet.  In  most  of  the  lowan  drift  area, 
the  leaching  of  the  drift  has  continued  to  the  present  without 
much  interruption.  Therefore,  in  order  to  make  proper  com- 
parisons, the  equivalent  of  the  leaching  of  the  loess  should  be 
added  to  the  leached  zone  of  the  Kansan. 

The  phenomena  of  weathering,  therefore,  seem  to  indicate  that 
there  is  in  northeastern  Iowa  a  drift  sheet  which  is  young  as  com- 
pared with  the  Kansan  drift. 

COMPARISON  WITH  THE  WISCONSIN  TILL. 

The  Wisconsin  till  was  examined  for  purposes  of  comparison 
at  several  points  from  Cerro  Gordo  county  south  to  Jasper 
county  and  along  the  Chicago,  Milwaukee  and  St.  Paul  railway 
across  the  southern  part  of  the  Wisconsin  drift  plain. 

In  practically  all  places  the  oxidation  of  the  Wisconsin  till  is 
to  a  light  buff  tint,  and  the  leached  zone  is  in  general  two  to  three 
feet  deep.  In  many  places  limestone  pebbles  are  present  at  or 
near  the  surface.  Locally  there  are  occurrences  of  loess  on  the 
Wisconsin  drift  but  the  amount  is  generally  negligible.  The  to- 
pography of  the  Wisconsin  is  typically  glacial  and  the  amount  of 
erosion  is  slight-  except  near  major  streams.  There  seems  to  be 
little  ground  for  doubt  that  the  lowan  drift  is  distinctly  older 
than  the  Wisconsin. 


THE   SUPER-KANSAN  GUMBO  89 

CHAPTER  III 

THE    SUPER-KANSAN    "GUMBO,"    ITS    CHARACTER,    RELA- 
TIONS, AND  SIGNIFICANCE. 

In  the  Kansan  Drift  Area 

An  overlying  later  till  may  not  be  distinctly  separable  in  many 
places  from  an  underlying  earlier  till,  especially  if  no  interglacial 
deposits  or  weathered  zone  have  survived  the  abrasion  of  the 
later  ice  sheet.  Nevertheless,  it  would  be  strange,  if,  in  an  area 
as  large  as  9,000  square  miles,  and  with  the  lowan  drift  as  thin 
as  has  been  described  there  should  not  be  found  unmistakable 
evidence  of  separation  from  the  Kansan  till. 

A  number  of  exposures  have  been  found  in  northeastern  Iowa 
showing  what  appear  to  be  remnants  of  the  super-Kansan 
" gumbo"  with,  in  some  places,  a  black  carbonaceous  layer  rep- 
resenting an  old  soil  at  the  top  and  above  this  a  later  till  of  mod- 
erate thickness.  In  these  places  the  supposed  lowan  till  is 
clearly  separated  from  the  older  drift.  The  character,  distribu- 
tion, and  mode  of  origin  of  the  super-Kansan  '  *  gumbo ' '  of  south- 
ern Iowa  are  to  be  discussed  by  Doctor  Kay  in  a  forthcoming 
paper.  A  preliminary  paper  has  been  published  already  by  him.6 
So  important  are  the  occurrences  of  " gumbo"  of  this  age  to 
the  question  of  the  differentiation  of  a  post-Kansan  drift  in 
northeastern  Iowa  that  a  brief  description  of  "gumbo"  expos- 
ures observed  by  the  writers  is  presented  here. 

Gumbo  Loess 

Loess  Gumbo 

Original  Kansan  dnft_piair,_  _ 


.   5. — Diagram  showing  relations  of  super-Kansan   "pumbo"  and  of  loess  to  rem- 
nants of  the  original  Kansan  drift  plain. 

Overlying  the  Kansan  till  on  the  uplands,  that  is,  on  remnants 
of  the  original  Kansan  plain  (figure  5)  throughout  much  of 
southern  Iowa  is  a  deposit  of  clay  which,  for  want  of  a  better 
name,  may  be  called  " gumbo."7  This  clay  is  dense,  sticky,  and 

'Kay,   Geo.    F.,    Some  Features   of  the   Kansan   Drift   in   southern   Iowa:    Bull.    Geol. 

™ Professor' Kay  baa  recently  proposed  the  name  "gumbotil"  for  this  and  similar 
deposits  See  Kay,  Geo.  F.,  Gumbotil,  a  new  term  in  Pleistocene  geology:  Science, 
N.  S.,  Vol.  XLIV,  pp.  637-638,  1916. 


90  THE  IOWAN  DRIFT 

very  slippery  when  wet.  It  is  generally  noncalcareous  and  dull 
gray  in  color.  Sometimes  the  color  is  gray  mottled  with  brown 
and  the  upper  part  is  oxidized  to  a  reddish  or  brownish  tint.  It 
has  not  the  loose  porous  texture  of  loess  and  the  sun-dried  face 
of  the  exposure  generally  differs  from  that  of  loess  in  being 
checked  by  sun  cracks.  A  fresh-fractured  surface  of  a  lump  of 
" gumbo"  often  shows  minute  pellets,  a  millimeter  or  so  in 
diameter,  of  clay,  or  sometimes  of  oxide  of  iron  or  manganese 
dioxide,  such  as  characterize  the  so-called  " buckshot"  clays.  Re- 
moval of  the  pellets  leaves  the  surface  pitted  with  little  concave 
depressions. 

There  are  places  where  the  "gumbo"  is  rather  sandy,  though 
even  here  a  sticky  clay  matrix  makes  the  grains  adhesive  rather 
than  loose ;  so  also  the  clay  may  contain,  in  patches,  small  angu- 
lar bits  of  feldspar,  quartz,  and  other  minerals  such  as  might  re- 
sult from  the  disintegration  of  included  granite  pebbles  or 
bowlders.  Some  instances  are  reported  by  Doctor  Kay  of  granite 
bowlders  being  included  and  still  retaining  their  form  though  so 
much  disintegrated  as  to  be  easily  cut  through  by  a  pick  or  spade. 
The  "gumbo"  is  nowhere  very  stony  but  it  generally  contains 
scattered  small  pebbles,  mostly  less  than  one  inch  in  diameter. 
These  are  predominantly  of  chert  and  quartz  but  with  these  are 
occasional  crystallines  and  quartzites.  An  estimate  of  pebbles 
collected  from  a  road  cut  in  the  "gumbo"  one-half  mile  south  of 
Russell,  Lucas  county,  showed  the  following: 

Per  cent 

Quartz 38.3 

Chert    38. 

Quartzite 8.3 

Granite 8.3 

Basalt 8.3 

Fine-grained    granite 1.6 

100.0 

Careful  examination  of  numerous  exposures  shows  no  lami- 
nation of  the  clay  such  as  usually  characterizes  waterlaid  silts 
and  shows  no  definite  line  of  demarcation  separating  this  clay 
from  the  Kansan  till  below.  The  change  from  the  stony  till  to 
the  less  stony  "gumbo"  above  takes  place  in  a  narrow  zone  but 
it  seems  clearly  to  be  one  of  gradation.  The  till  may  be  leached 
of  its  calcareous  material  for  a  few  feet  below  the  base  of  the 


THE  GUMBO  IN  THE  KANSAN  AREA  91 

"gumbo"  or  it  may  be  highly  calcareous  nearly  or  quite  to  the 
narrow  zone  of  transition.  The  limestone  and  dolomite  pebbles 
and  most  of  the  crystallines  become  smaller  and  smaller  from 
the  base  of  the  transition  zone  up  into  the  "gumbo,"  where  they 
disappear;  and  the  few  crystalline  pebbles  which  remain  are 
usually  badly  decomposed  and  are  smaller  and  still  fewer  toward 
the  top  of  the  "gumbo."  This  condition  gives  rise  to  the  sug- 
gestion that  the  "gumbo"  is  not  a  distinct  and  later  deposit  but 
that  it  is  the  residuum  of  thorough  weathering  and  long  leaching 
of  the  upper  part  of  the  Kansan  till. 

The  "gumbo"  where  seen  by  the  writers  ranges  in  thickness 
from  a  few  feet  to  eighteen  feet.  If  it  really  is  the  residuum  of 
the  upper  part  of  the  Kansan  till  after  the  more  readily  soluble 
constituents  have  been  removed  by  leaching,  it  evidently  rep- 
resents a  very  long  time  of  exposure  since  the  disappearance  of 
the  Kansan  ice  sheet. 

The  upper  part  of  the  "gumbo"  is  generally  colored  reddish  or 
brownish  as  the  result  of  oxidation  and  hydration  and  where  the 
gray  clay  has  been  burned  for  brick  or  railroad  ballast,  it 
changes  to  a  red  color.  The  part  of  the  till  immediately  beneath 
the  "gumbo"  is  also  generally  oxidized  orange,  brownish,  or 
buff,  and  the  latter  tint  may  continue  downward  fifteen  or  twenty 
feet  before  .grading  into  the  original  blue-gray  or  blue-black 
color  of  the  unoxidized  till. 

With  some  exceptions,  which  may  be  the  result  of  redeposi- 
tion,  the  "gumbo"  lies  on  the  upland  remnants  of  the  Kansan 
drift  plain.  It  does  not  extend  down  the  slopes  but  is  cut  off  by 
erosion.  From  this  it  is  inferred  that  the  "gumbo"  was  developed 
(possibly  when  the  plain  was  low-lying)  before  any  considerable 
amount  of  dissection  of  the  Kansan  plain  had  been  accomplished. 
If  all  these  suggestions  are  really  true,  it  is  apparent  that  the 
interval  between  the  Kansan  and  Illinoian  stages  of  glaciation, 
the  Yarmouth  interval,  was  of  very  long  duration,  for  studies  in 
southeastern  Iowa  and  western  Illinois  (see  page  199)  show  that 
the  super-Kansan  "gumbo"  there  underlies  the  Illinoian  drift. 

In  the  Kansan  area,  this  "gumbo"  lies  on  top  of  the  Kansan 
drift,  and  near  the  lowan-Kansan  border  it  underlies  loess. 
Wherever  the  loess  is  more  than  six  or  eight  feet  thick,  its  base 


92  THE   IOWAN   DRIFT 

is  calcareous,  whereas  the  " gumbo"  is  leached  and  the  upper  one 
foot  or  so  is  oxidized  to  a  brownish  gray  with  reddish  specks 
scattered  promiscuously.  There  is  no  doubt  that  the  ''gumbo"  is 
much  older  than  the  loess. 

These  various  questions  will  be  considered  by  Doctor  Kay  in 
his  forthcoming  paper.  Whatever  may  be  the  final  conclusion 
in  regard  to  them,  one  thing  seems  to  be  clear,  the  ' '  gumbo ' '  has 
so  wide  a  development  on  the  remnants  of  the  Kansan  plain  that 
whatever  its  origin  it  seems  to  mark  fairly  definitely  the  strati- 
graphic  horizon  of  the  original  top  of  the  Kansan  drift,  even  in 
the  lowan  drift  area.8  The  only  qualification  of  this  statement 
as  far  as  the  relations  of  the  lowan  drift  are  concerned  arises 
from  the  fact,  (discussed  in  another  connection)  that  a  similar 
bed  of  " gumbo"  occurs  in  places  at  the  top  of  the  Nebraskan 
drift.  The  finding  of  somewhat  similar  deposits  at  the  top  of  the 
Illinoian  drift  while  affecting  the  interpretation  as  to  relative 
age  of  the  lowan  and  Illinoian  drifts  does  not  directly  affect  the 
question  of  the  lowan  drift  being  a  distinct  post-Kansan  drift 
sheet- 
In  the  lowan  Drift  Area 

In  the  lowan  drift  area  a  number  of  exposures  of  " gumbo," 
probably  the  super-Kansan  " gumbo,"  have  been  observed,  and 
overlying  this  is  a  deposit  of  glacial  till.  If  this  ".gumbo"  is 
really  super-Kansan  the  drift  over  it  is  clearly  the  product  of 
a  distinct  ice  invasion  of  post-Kansan  age.  This  upper  till  the 
writers  believe  to  be  the  lowan  till.  This  "gumbo"  is  identical 
in  character  with  that  found  on  the  Kansan  of  southern  Iowa.  It 
has,  in  places,  a  black  carbonaceous  layer,  an  old  soil,  at  the  top. 
So  far  as  observed  it  is  noncalcareous  while  the  overlying  till  is 
in  some  places  seen  to  be  highly  calcareous.  At  other  exposures 
the  drift  is  so  thin  that  it  has  been  leached  of  its  calcareous  con- 
stituents. The  observed  exposures  of  the  "gumbo"  are  mostly 
in  the  higher  parts  of  the  lowan  drift  area,  in  those  places  where 
it  would  be  expected  that  remnants  of  the  original  Kansan  plain 
might  be  preserved.  These  exposures  are  mostly  in  recently- 
made  cuts  for  electric,  steam,  and  wagon  roads,  so  that  but  few 

"For  purpose  of  record  and  to  make  the  data  readily  accessible  for  study,  there  are 
inserted  in  Appendix  B  notes  on  exposures  of  the  super-Kansan  "gumbo"  in  the  area 
seen  by  the  writers  immediately  south  and  east  of  the  lowan  drift  area. 


THE   GUMBO   IN   JONES   COUNTY  93 

of  them  seem  to  have  been  observed  during  the  earlier  studies  of 
the  area  and  such  as  were  seen  were  not  recognized  as  having  the 
significance  now  attached  to  them.  Besides  being  observed  in 
exposures,  the  ".gumbo"  was  encountered  in  some  of  the  borings 
made  by  the  writers.  These  new  items  of  evidence  are  important 
as  lending  definite  support  to  the  theory  of  post-Kansan  glacia- 
tion  in  northeastern  Iowa.  Considering  the  fact  that  only  a  very 
small  part  of  the  roads  of  the  lowan  area  were  actually  traversed 
during  these  two  field  seasons,  the  study  being  in  the  nature  of  a 
review  rather  than  a  detailed  survey,  it  is  not  remarkable  that  so 
small  a  number  of  exposures  of  the  gumbo  were  found.  Further 
examination  throughout  the  area  along  the  roads  not  already 
traversed  may  yield  additional  data.  So  important  is  the  evi- 
dence in  hand  that  detailed  descriptions  of  the  occurrences  noted 
are  given  herewith.  They  may  thus  be  compared  with  the  de- 
scriptions of  occurrences  of  " gumbo"  in  the  Kansan  area  and 
in  the  Illinoian  drift  area.  (See  Appendix  B.) 


Fig  e  — Diagrammatic  section  across  ridge  south  of  Langworthy,  Iowa,  showing 
relations  of  loess:  (1)  lowan  till;  (2)  Yarmouth  soil  and  super-Kansan 
"gumbo";  (3)  Kansan  drift;  (4)  earlier  deposits. 

JONES    COUNTY. 

One  of  the  most  significant  exposures  is  in  Jones  county  on  the 
top  of  the  ridge  between  Monticello  and  Anamosa.  The  relations 
are  shown  in  figure  6.  The  general  relation  of  this  ridge  are 
shown  on  a  smaller  scale  in  figure  1. 

The  exposure  is  south  of  Langworthy  and  about  five  miles 
northeast  of  Anamosa  in  the  south  slope  of  a  lobe  of  the  ridge,  m 


94  THE   IOWAN   DRIFT 

Jones  county,  Wayne  township,  (Township  8.5  North,  Range  3 
West,  section  30  near  the  middle  of  the  north  line).  The  beds  ex- 
posed in  the  road  cut  and  penetrated  by  boring  with  an  auger  are 
as  follows  (see  A,  figure  6) : 

DRIFT   SOUTH   OF  LANGWORTHY,   IOWA. 

Feet. 

5.    Loess,    leached    

4.  Till  (lowan)  brown,  rather  sandy,  leached 

3.  Soil    band,    black     to     brown,     with     carbonaceous 

matter    • few  inches 

2.  "Gumbo"   (super-Kansan),  noncalcareous,  gray,  dense 

clay,  very  sticky  when  w'et 8-10 

1.  Till  (Kansan)  is  slightly  exposed  at  foot  of  the  slope. 

Across  the  sag  to  the  south  (B,  figure  6)  similar  relations  are 
shown  at  the  same  level.  The  cut  and  boring  here  showed  : 

DRIFT  SOUTH  OF  LANGWORTHY,  IOWA. 

Feet. 

5.  Loess    , 5 

4.  Till,   (lowan),  brown,  leached 5^4 

3.  Soil  band,  black few  inches 

2.  "Gumbo"  (super-Kansan),  gray,  noncalcareous  clay..  4 

1.    Till   (Kansan) ,  rusty,  brown,  leached 4 

1.    Till   (Kansan)   calcareous. 

The  "gumbo"  is  like  that  overlying  the  Kansan  drift  in 
southern  Iowa  and  is  believed  to  mark  the  same  horizon. 

Neighboring  wells  show  this  ridge  to  be  wholly  of  drift  and  to 
overlie  an  old  valley  cut  in  the  rock.  Numerous  wells  have  pene- 
trated 200  to  400  feet  or  more  of  drift  and  underlying  sand  and 
gravel.  It  is  quite  possible  that  this  includes  both  Kansan  and 
pre-Kansan,  besides  lowan,  deposits.  Farther  southeast  the 
ridge  is  much  dissected  and  numerous  cuts  show  the  highly 
oxidized  upper  part  of  the  Kansan  till  but  with  no  overlying  later 
till.  The  loess-mantled  ridge  is  cut  by  sharp  ravines  where 
crossed  by  the  Anamosa-Monticello  road,  on  which  are  the  ex- 
posures described  above,  but  farther  northwest  the  surface  be- 
comes smoother  and  less  dissected.  These  relations  indicate  that 
the  ridge  of  Kansan  drift  was  overridden  by  the  lowan  ice  as  far 
southeast  as  this  road  but  not  much  if  any  farther.  The  buried 
soil  and  "gumbo"  thus  mark  the  horizon  of  the  original  Kansan 
plain  which  is  here  nearly  1,000  feet  above  sea  level. 


THE  GUMBO  IN  DELAWARE  COUNTY  95 

DELAWARE  COUNTY. 

In  the  southwestern  part  of  Delaware  county  where  the 
mantled  topography  is  very  well  developed  there  is  a  belt  of  thick 
drift  and  here  the  super-Kansan  "gumbo"  and  soil  are  found  be- 
neath the  lowan  till.  The  '  *  gumbo ' '  was  found  by  Mr.  Leighton, 
exposed  about  five  miles  northeast  of  Eyan  (Milo  township, 
Township  88  North,  Eange  5  West,  section  34,  west  line  of 
southwest  quarter)  in  a  road  cut  in  a  small  hill  on  top  of  the 
ridge  at  1060  ±  feet  above  sea  level.  The  cut,  together  with  a 
boring,  showed  the  following: 

DRIFT  NORTHEAST  OF  RYAN,   IOWA. 

Feet. 

.6.     Soil,   pebbly    1 

•    4.     Till  (lowan),  bright  yellow,  calcareous  nearly  to  top 3 

3.  Silt,  gray  to  drab,  slightly  calcareous. . .  — 3 

2.  "Gumbo"   (super-Kansan),  drab  to  ashen-gray  silt,  contains 
considerable  grit  and  some  pebbles,  noncalcareous 4 

1.  Till  (Kansan),  reddish  brown  at  top  with  clay  ironstones 
and  ferruginous  streaks,  leached  five  feet,  calcareous  be- 
low          5+ 

This  hillock  is  one  of  a  group  having  somewhat  the  appearance 
of  a  moraine. 

In  a  boring  on  the  ridge  crest  on  the  opposite  side  of  Lime 
creek  valley  at  a  point  about  two  miles  southeast  of  Ryan  (Hazel 
Green  township,  Township  87  North,  Range  5  West,  section  29, 
north  line  of  northwest  quarter)  the  following  similar  series  of 
beds  were  penetrated: 

DRIFT  SOUTHEAST  OF  RYAN,  IOWA. 

Feet. 

5.     Sand    4y2 

4.  Loess,  yellow,  leached % 

3.  Till     (lowan),    yellow,    leached 1 

2.  Silt,  very  dark  gray,  loesslike  in  texture,  noncalcareous 1% 

1.     "Gumbo"-like  clay  (super-Kansan),  gray,  mottled  brownish, 

containing    quartz    pebbles    and    somte    decomposed    green- 
stones and  granite  pebbles,  penetrated y% 

This  is  on  the  highest  part  of  the  broad  ridge  at  1080*  feet 
above  sea  level,  in  a  district  where  wells  show  160  feet  of  drift. 

Later,  in  company  with  R.  D.  Salisbury,  Frank  Leverett,  and 
Gr.  F.  Kay  Mr.  Alden  observed  several  exposures  (at  1040*  feet 
above  sea  level)  in  cuts  on  the  north-south  road  between  sections 
28  and  29,  32  and  33,  showing: 


96  THE   IOWAN   DRIFT 

DKIFT  SOUTHEAST  OF  RYAN,  IOWA. 

3.    Till   (lowan),  leached,  a  few  feet. 
2.     Soil,  black,  carbonaceous,  a  few  inches. 

1.     "Gumbo"     (super-Kansan?),    dense,    gray,    noncalcareous    clay 
containing  small  pebbles;   exposed  for  a  few  feet. 

BUCHANAN  COUNTY. 

On  going  northwest  along  the  same  belt  of  relatively  high 
country  and  thick  drift  some  exposures  were  found  in  eastern 
Buchanan  county. 

About  four  miles  southwest  of  Masonville  (Middlefield  town- 
ship, Township  88  North,  Range  7  West,  section  3,  west  line)  the 
north-south  road  crosses  the  crest  of  a  high  ridge,  the  continua- 
tion of  the  belt  of  thick  drift  seen  farther  southeast.  The  crest 
stands  1,100  feet  above  sea  level.  Wells  on  this  ridge  are  said  to 
penetrate  200  to  265  feet  of  drift  so  that  it  appears  that  a  valley 
cut  in  the  rock  underlies  the  ridge.  A  cut  and  boring  on  the  crest 
of  the  ridge  showed : 

DRIFT  SOUTHWEST  OF  MASOXVILLE,  IOWA. 

Feet. 

Soil,  black,  sandy,  pebbly  loam 1 

Till  (lowan),  brownish  yellow,  leached  four  feet  and  calcareous 
below    6+ 

.  At  a  point  fifty  to  sixty  feet  below  the  top  of  the  south  slope  a 
bed  of  "gumbo"  was  slightly  exposed  in  the  ditch  (at  1050± 
feet  above  sea  level)  beneath  a  thin  covering  of  till.  The  ditch 
and  boring  showed : 

DRIFT  SOUTHWEST  OF  MASOXVILLE,  IOWA. 

Feet. 

Loam,  black,  pebbly 1% 

Till    (lowan),   brown,    leached 2 

"Gumbo"    (super-Kansan)   dense,  sticky,  gray,  noncalcareous..   3+ 

•  If  one  may  judge  from  the  relations  noted  elsewhere  the 
"gumbo"  probably  extends  back  horizontally  into  the  ridge  so 
that  there  may  be  fifty  feet  of  lowan  till  above  it.  The  under- 
lying till  is  not  exposed  but  the  wells  of  the  region  indicate  that 
there  is  probably  a  considerable  thickness  below  the  horizon  of 
the  "gumbo." 

About  six  miles  north  of  this  place  (Fremont  township,  Town- 
ship 89  North,  Range  7  West,  section  11,  west  line  of  northwest 
quarter)  in  the  same  high  belt  of  thick  drift,  a  boring  on  the  slope 


GUMBO  IN  LINN  COUNTY  97 

of  the  ridge  about  fifty  feet  below  the  top  (at  1,090-1,100  feet 
above  tide)  showed: 

DRIFT  NOKTHWEST  OF  MASONVILLE,  IOWA. 

Feet. 
Till  (lowan),  brown,  leached  and  very  stony  ................  1% 

"Gumbo"    (super-Kansan),   dense,    gray,   noncalcareous   clay  4 
Clay,   sandy,    gray  .........................................  2+ 

A  boring  on  the  crest  of  the  ridge  a  mile  farther  north  at  1,140 
feet  above  sea  level  showed  : 

DRIFT  NORTHWEST  OF  MASONVILLE,  IOWA. 

Feet. 
Soil,  black    ..........................................  1 

Till   (lowan),  yellow,  leached  ............  ............         '.'.  5 

Till,  calcareous  below 


Here  again  it  appears  there  may  be  a  considerable  thickness 
of  lowan  drift  above  the  horizon  of  the  "  gumbo"  in  the  body  of 
the  ridge  though  it  is  very  thin  at  the  point  of  outcrop  in  the 
slope. 

A  cut  on  the  Chicago,  Anamosa  and  Northern  railway  one  mile 
east  of  Kiene  in  Middlefield  township,  Township  88  North,  Range. 
7  West,  section  34,  southwest  quarter,  exposed  the  following  : 

DRIFT  ON  CHICAGO,  ANAMOSA  &  NORTHERN  RAILWAY  EAST  07  KIENE,  IOWA. 

Feet. 


6.     Humus,  dark,  and  brown  pebbleless  clay 

5.     Line  of  pebbles. 

4.     Till,  buff  to  brown,  leached,  clayey  .....................  4-6 

3.     Till,    similar   to   above,   but   calcareous,    with    abundant 

limestone   pebbles    ...................  .  .................      2 

—    Distinct  line  of  division,  not  a  gradation  zone. 

2.     Clay,  dense,  dark  slate  colored,  ashen  gray  in  places  and 

oxidized    brown    along   joints    and    bedding    or   cleavage 

planes.     Suggests  the  super-Kansan  "gumbo"  ............      5 

1.     This  grades  down  into  dark,  slate-colored,  pebbly  clay  till, 

brown   in  places,  noncalcareous. 

The  lower  till  No.  1,  resembles  the  unoxidized  Kansan  except 
in  being  noncalcareous  where  tested.  The  upper  till,  Nos.  3  and  4, 
above  the  distinct  division  line,  is  like  that  generally  present  at 
the  surface  in  the  lowan  area. 

LINN  COUNTY. 

In  Linn  county  about  four  miles  northeast  of  Center  Point 
(Otter  Creek  township,  Township  85  North,  Range  7  West,  sec- 
tion 4,  i-'onlli  line)  a  boring  made  in  a  shallow  road  cut  on  the 
gently  undulating  plain  showed  the  following  : 


98  THE   IOWAN   DRIFT 

DBIFT  NORTHEAST  OF  CENTER  POINT,  IOWA. 

Feet. 

Till   (lowan),  leached   3-4 

Clay,  yellowish  gray,  gritty  and  noncalcareous  and  of  texture 
suggesting    super-Kansan   "gumbo"    3 

Three  miles  northwest  of  Central  City  (Jackson  township, 
Township  86  North,  Range  6  West,  section  21,  north  of  center) 
" gumbo"  is  exposed  beneath  till  in  a  road  cut  near  the  top  of 
the  east  slope  of  the  hill.  The  road  cut  and  test  bores  made  in 
the  bottom  of  the  cut  show  the  following  beds : 

DRIFT  NORTHWEST  OF  CENTRAL  CITY,  IOWA. 

Feet. 

4.  Soil,  loamy,  pebbly  1% 

3.    Till    (lowan),  brownish  yellow,   leached 2~y2 

3.  Till    (lowan),   calcareous,  yellow,  grading   downward   into 
gray    6 

2.  "Gumbo"    (super-Kansan),   noncalcareous,   black   soil   with 
wood  at  top,  dark  gray  below,  with  "buckshot"  texture  and 
rare    small    pebbles    of    chert    and    quartz     (one    dolerite 
found)     3 

1.  Sand  and  gravel. 

This  exposure  is  about  twenty-five  feet  below  the  top  of  the 
ridge  and  about  120  feet  above  Wapsipinicon  river,  one  mile  dis- 
tant. The  relations  here  and  at  the  following  exposures  suggest 
that  a  thin  bed  of  Kansan  till  underlain  by  sand  or  sand  and 
gravel  has  been  wholly  changed  to  "gumbo." 

In  the  southwestern  part  of  the  county  four  miles  east  of 
Atkins  (Linn  county,  Clinton  township,  Township  83  North, 
Range  8  West,  section  16,  southwest  quarter)  a  cut  on  the 
Chicago,  Milwaukee  &  St.  Paul  railway  through  the  southeast 
end  of  a  paha  shows  the  following : 

DBIFT  EAST  OF  ATKINS,  IOWA. 

Feet. 

5.  Loess,  buff,  calcareous  in  lower  part 15 

4.  Till  (?)    (lowan?),  reddish  to  yellow  leached  pebbly  clay. 0-1 

3.  "Gumbo"    (?),  soft,  dull  brownish  to  reddish  gray  clay, 
noncalcareous    and    with    some    small    pebbles    and    sand 
grains     2y2-3 

2.  Sand   and   gravel,   buff 3 

1.     Till  (Kansan?),  leached,  with  rotten  pebbles  and  bowlders  1 
1.     Till   (Kansan?) ,  gray,  calcareous   1-2 

BENTON  COUNTY. 

Three  or  four  miles  southeast  of  Brandon  (Harrison  township, 
Township  86  North,  Range  10  West,  section  12,  northwest  quar- 


GUMBO  IN  BLACK  HAWK  COUNTY  99 

ter)  the  deeper  part  of  a  cut  on  the  electric  railroad,  on  top  of  the 
ridge  (at  QOC^  feet  above  sea  level)  showed  the  following: 

DRIFT  SOUTHEAST  OF  BRANDON,  IOWA. 

Feet. 

5.     Soil,  dark,  pebbly  loam  %-l 

4.     Gravel,   stratified,  rusty  reddish  brown,  pebbles  somewhat 

decayed,  clay  ironstone  present,  noncalcareous 0-4 

3.     Sand  and  gravel,  brown,  cross-bedded,  noncalcareous 3-4 

2.  "Gumbo",  dense,  sticky,  gray,  noncalcareous,  pebbleless  clay  3 

1.  Grading  down,  in  one  part,  into  gray  clayey  sand  to  loose 
sand.     In  the  lower  part  a  bright  yellow  streak  and  below 
this  the  nearly  white  sand,  total  exposed 6 

The  "gumbo"  (No.  2)  resembles  the  super-Kansan  "gumbo" 
of  southern  Iowa,  but  it  is  overlain  by  sand  and  gravel  and 
grades  down  into  loose  sand. 

Two  miles  north  of  Newhall  (Eldorado  township,  Township 
83  North,  Eange  10  West)  (at  940±  feet  above  tide)  "gumbo" 
was  observed  in  cuts  on  the  road  north  and  west  of  the  south- 
east corner  of  section  1  about  ten  feet  below  the  top  of  the  slopes. 
Cuts  and  borings  gave  the  following  section : 

DRIFT  NORTH  OF  NEWHALL,  IOWA. 

Feet. 

3.  Till  (lowan),  yellow,  leached  4 

2.  Silt,  light  gray,  noncalcareous    % 

1.  "Gumbo"  (super-Kansan?),  black  with  carbonaceous  matter  at 
top,  dark  gray  below,  dense  rubber-like  clay,  noncalcareous, 
exposed  : A  few  feet 

This  is  on  one  of  the  highest  tracts  in  this  part  of  the  country. 
The  "gumbo"  is  cut  off  by  the  slope,  apparently  having  been 
eroded  prior  to  the  deposition  of  the  upper  till  which  now 
mantles  the  slope  and  covers  the  "gumbo." 

Three  miles  south  of  Vinton  (Eden  township,  Township  84 
North,  Eange  10  West,  section  3)  a  boring  on  the  ridge  just  south 
of  the  northwest  corner  penetrated  the  following : 

DRIFT  SOUTH  OF  VINTON,  IOWA. 

Feet. 

4.  Loess,  brownish  yellow,  leached   2 

3.  Till  ( lowan) ,  brownish  yellow,  leached  3 

2.  "Gumbo"-like  clay   (super-Kanson),  dark  gray,  leached 1 

1.     Till  (Kansan),  brownish  yellow,  leached;  penetrated 2 

BLACK  HAWK  COUNTY. 

In  the  southwestern  part  of  Black  Hawk  county  the  following 
was  found  in  the  Chicago  &  North  Western  railway  cut  one-half 
mile  northwest  of  Voorhies.  Part  of  the  section  was  determined 


100  THE  IOWAN   DRIFT 

by  boring  at  two  different  levels,  the  lower  hole  reaching  a  depth 
of  five  and  one-half  feet  below  the  track. 

DBIFT  NORTHWEST  OF  VOOBHIES,   IOWA. 

Feet. 

7.    Clay,  loesslike  3y2 

6.     Till   (lowan),  buff,  leached,  clayey  3-3y2 

5.     Till  (lowan),  buff,  calcareous  iy2 

4.  Clay,  dense  bluish  gray,  noncalcareous,  containing  small 
quartz  pebbles;   "gumbo"   (?)    3-3*4 

3.  Clay  (Kansan  till),  brown  to  gray,  leached,  pebbly % 

2.  Clay,   brownish   gray,  mostly    leached   but   calcareous   in 
spots  or  with  small  limestone  pebbles,  crystalline  pebbles 
rotten    (Kansan  till)    7 

1.  Till  (Kansan),  dense,  buff,  calcareous   5% 

While  the  part  of  this  section  determined  by  the  two  borings 
may  not  be  exactly  continuous,  it  seems  probable  that  Nos.  5  and 
6  comprise  the  lowan  till.  Number  4  is  like  the  super-Kansan 
"gumbo,"  and  Nos.  1,  2,  and  3  are  probably  Kansan  till,  includ- 
ing the  gradation  zone. 

This  cut  was  examined  by  Prof.  M.  F.  Arey  and  described 
somewhat  differently  in  his  report9.  At  the  time  of  the  writers' 
visit  in  1914  the  section  was  obscured  by  vegetation. 

FAYETTE   COUNTY. 

To  the  northwest,  in  Fayette  county,  one  of  the  best  exposures 
was  found  five  miles  west  of  West  Union  (Windsor  township, 
Township  94  North,  Eange  9  West,  section  16,  north  line  of  the 
northeast  quarter),  in  a  road  cut  through  a  small  ridge  or  lobe  of 
the  slope  at  1200±  feet  above  sea  level.  The  cut  and  boring 
showed  the  following: 

DRIFT  WEST  OF  WEST  UNION,  IOWA. 

Feet.  Inches. 

5.  Till    (lowan),  yellow,  calcareous  in  lower  part..   10 

4.  Clay,  loesslike,  gray  above,  rusty  brown  in  lower 
part    1% 

3.  Soil,  black  carbonaceous  layer 1-3 

2.  "Gumbo"    (super-Kansan)    dense,   gray   clay,   non- 
calcareous   5± 

1.    Till  (Kansan),  rusty  brown,  leached 3y2 

1.     Till    (Kansan),  calcareous. 

The  soil  and  "gumbo"  were  exposed  at  both  ends  of  the  cut, 
but  were  below  the  level  of  the  road  in  the  middle  of  the  cut. 
A  boring  through  No.  4  in  the  bottom  of  the1  middle  of  the  cut 
showed  that  the  soil  (No.  3)  and  "gumbo"  (No.  2)  really  extend 

•Iowa  Geological  Survey,  Vol.  XVI,  p.  443,  1905. 


GUMBO  IN  HOWARD  COUNTY  101 

through  the  ridge.  A  boring  in  the  bottom  of  the  ten-foot  cut  on 
the  east  line  of  the  northeast  quarter  of  the  same  section  showed 
the  black  soil  No.  3  and  "gumbo"  No.  2  to  be  present.there  also. 
Two  miles  south,  on  the  west  line  of  the  northwest  quarter  of 
section  27  (at  1220  feet  above  sea  level)  a  boring  with  the  auger 
penetrated  the  following: 

DRIFT  EAST  OF  HAWKEYE,  IOWA. 

Feet. 

4.     Soil,  dark,  pebbly. 
3.     Till    (lowan),   yellow,   sandy,   leached 3 

2.  Soil,  dark,  carbonaceous  band. 

1.  "Gumbo"    (super-Kansan),   dense,   tough,   rubber-like   gray 
clay    3+ 

These  occurrences  of  the  buried  soil  and  "gumbo"  are  in  the 
higher  parts  of  the  gently  undulating  upland  plain  at  IWfl*  feet 
above  sea  level. 

HOWARD  COUNTY. 

Still  farther  north  near  the  eastern  border  of  the  lowan  area 
in  Howard  county,  an  exposure  in  the  new  pit  at  the  brick  yard 
just  north  of  the  railroad,  together  with  a  boring  made  in  the 
bottom,  showed : 

DKIFT  AT  CEESCO. 

Feet. 

3.  Soil,  pebbly   V2-l 

2.  Till   (lowan),  brownish  to  yellow,  sandy,  leached,  with 
crystalline    pebbles    and    bowlders    up    to    two    feet    in 

diameter 2-3 

1.     Clay,   "gunabo"-like,    (super-Kansan),       noncalcareous, 

'"buckshot"  texture  in  places,  upper  few  inches  to  one 
foot  light  drab,  darker  drab  two  to  four  feet  (as  though 
colored  by  carbonaceous  material),  light  greenish  drab, 
then  mottled  brownish  yellow  to  drab  below 7+ 

In  this  connection  the  following  description  of  exposures  at 
Cresco  from  the  notes  of  B.  I1.  Chamberlin,  made  July  18, 1907,  is 
of  interest.  This  shows  the  presence  of  calcareous  till  (Kansan) 
below  the  gummy  clay. 

Cresco  brick  yard. — South  pit,  this  is  the  deepest  pit  but  is  not 
used  at  present.  At  northwest  end  of  this  pit  the  bank  shows 
three  and  one-half  feet  of  yellow  brown  lowan  drift  noncal- 
careous throughout.  The  upper  portion  merges  into  the  surface 
dirt.  I  failed  to  find  a  single  limestone  pebble  in  it  even  after  a 
careful  search.  There  are  frequent  cherts  and  a  good  many 
quartzites  and  the  tiny  pebbles  of  gray  or  white  granite  and  other 


102  THE   IOWAN   DRIFT 

light-colored  igneous  rocks  which  are  so  characteristic  of  the 
lowan.  Below  the  lowan  is  a  nondescript  gummy  clay  mixed 
with  some  sandy  layers  which  looks  very  much  like  interglacial 
material.  The  gummy  clay  contains  many  of  the  polished  quartz 
pebbles  and  may  have  been  washed  in  from  a  .gummy  portion  of 
the  older  drifts  during  the  Buchanan  period.  It  is  noncalcare- 
ous. 

I  looked  over  the  bank  of  lowan  very  carefully,  noting  care- 
fully several  hundred  pebbles — in  fact  all  that  could  be  seen  in 
some  twenty  feet  of  bank,  collecting  all  the  suspicious  cherts  that 
might  possibly  prove  to  be  still  calcareous  but  though  I  split  open 
and  tested  with  acid  fifty  or  more  of  these  (chiefly  cherts  for  I 
could  spot  the  igneous  rocks  readily)  there  was  not  a  single 
pebble  that  effervesced  to  the  slightest  degree. 

The  bottom  of  the  brickyard  is  strewn  with  numerous  large 
bowlders  of  the  lowan  .type,  doubtless  encountered  in  and  left 
behind  when  that  drift  was  removed.  At  the  lowest  point  in 
the  pit  a  prospect  hole  has  been  dug  some  feet  deeper  (how  much 
is  not  apparent  since  it  is  filled  with  water  and  is  now  a  small 
pond).  The  material  taken  out  has  been  piled  nearby.  It  is 
found  to  contain  abundant  limestone  pebbles,  but  this  comes 
from  below  the  gummy  stuff  and  the  layer  of  sand  and  is  neither 
the  lowan  nor  the  clay  used  for  the  brick.  It  is  probably  Kansan 
drift.  The  foreman  volunteered  the  information  that  the  clay 
which  they  used  contained  no  lime  but  that  they  got  in  their 
prospect  lower  down  contained  limestone  pebbles  and  hence  was 
not  desirable. 

In  the  west  pit  the  lowan  drift  is  only  about  2  ft.  thick.  Then 
comes  a  horizon  of  bluish-grayish  brown  gummy  clay  with  lenses 
and  patches  of  gray  sand.  The  thickness  of  this  is  about  3  feet 
to  the  .floor  of  the  pit.  The  floor  of  the  pit  is  a  layer  of  grayish 
sand  which  is  not  desirable  and  avoided.  Below  this  as  shown 
in  the  other  pit  is  another  drift  containing  limestone  pebbles. 

MITCHELL  COUNTY. 

About  eight  miles  west  of  Osage  (Eock  township,  Township 
98  North,  Eange  18  West,  section  34,  middle  of  west  line)  a 
boring  on  a  low  slope  penetrated  mottled  gray  and  yellow,  dense, 
sticky  clay  with  few  pebbles.  This  clay  suggests  the  super- 
Kansan  "gumbo"  rather  than  the  normal  weathered  till.  Five 
feet  down  this  becomes  sandy  and  wet. 

A  few  miles  to  the  north  in  section  11  (south  line  of  the  south- 
east quarter),  a  boring  on  the  extensive  flat  plain  showed: 


GUMBO  IN  MITCHELL  COUNTY  103 

DRIFT  WEST  OF  MITCHELL,  IOWA. 

Feet. 

2.  Clay   humus,   black 

1.  "Gumbo,"    dense,    sticky,    gray,    noncalcareous    clay    con- 
taining few  small  pebbles g 

Near  the  underlying  limestone  the  clay  is  yellowish  in  color. 

A  cut  on  a  short  steep  slope  a  short  distance  east  of  this,  and 
about  three. miles  west  of  Mitchell,  together  with  a  boring1,  pene- 
trated nine  feet  of  "gumbo,"  dense,  tough,  rubber-like,  brown- 
ish, noncalcareous  clay.  There  is  no  overlying  till  (lowan)  at 
these  places  but  drift  pebbles  and  bowlders  scattered  over  the 
surface  show  that  the  ' '  gumbo ' '  has  been  overridden  by  later  ice. 

One  mile  north  of  Mitchell  (Mitchell  township,  Township  98 
North,  Eange  17  West,  section  5,  west  line  of  the  southeast 
quarter),  a  boring  on  the  flat  upland  plain  (at  1190±  feet  above 
sea  level)  penetrated,  beneath  two  feet  of  dark  loesslike  loam, 
the  same  dark  brown  to  gray,  dense,  noncalcareous  " gumbo" 
clay,  rusty  in  spots,  to  a  depth  of  nine  feet.  There  is  here  no 
overlying  till,  only  drift  pebbles  and  scattered  bowlders  one  to 
three  feet  in  diameter.  Two  miles  east  of  Mitchell  (section  11, 
west  line  of  the  southwest  quarter)  the  same  dense  brown  clay, 
with  " buckshot"  of  Mn02,  was  found  by  boring  beneath  five 
and  one-half  feet  of  loess  and  one  and  one-half  feet  of  sand. 

At  another  place  about  five  miles  northeast  of  Mitchell  (near 
the  northeast  corner  of  section  1)  a  boring  on  the  flat  plain 
revealed : 

DRIFT  NORTHEAST  OF  MITCHELL,  IOWA. 

Feet. 

3.  Humus,  black  clay 1% 

2.  'Clay,  gray,  loesslike,  no  pebbles  excepting  at  bottom 1 

1.  "Gumbo,"  dense,  brownish  gray,  noncalcareous  clay,  sandy 

at   bottom    5y2 

Again,  a  boring  one  and  one-half  miles  east  of  St.  Ansgar 
(at  1170  ±  feet  above  sea  level)  showed: 

DRIFT  EAST  OF  ST.  ANSGAR,  IOWA. 

Feet. 

3.  Soil,  black,  and  loess 1 

2.  Clay,    sandy,    brown,    with   some    pebbles    (possibly    lowan 
drift)     2 

1.     "Gumbo,"  dense,  sticky,  gray  to  brown,  noncalcareous  clay 
with  scattered  small  chert  pebbles  and  sand  grains 4% 


104  THE  IOWAN  DRIFT 

This  becomes  light  buff  in  color  at  the  bottom  near  the  under- 
lying limestone.  There  appears  to  be  but  little  glacial  drift  of 
any  kind  at  these  places.  The  nearly  flat  plain  may  be  part  of 
the  original  Kansan  upland,  which  escaped  erosion  and  on  which 
the  conditions  for  " gumbo"  development  existed. 

WORTH   COUNTY. 

In  borings  at  two  points  in  the  southeastern  part  of  Worth 
county  on  the  plain  east  of  Manly,  there  was  penetrated  very 
dense,  brownish  to  gray  clay,  noncalcareous,  and  containing  few 
small  pebbles.  This  suggests  the  "  gumbo  "-like  clay  found 
farther  east  in  Mitchell  county,  and  may  really  be  the  long 
weathered  upper  part  of  the  Kansan  till  with  no  overlying 
lowan  drift.  A  short  distance  from  one  of  these  places,  that  is, 
in  the  low  slope  just  east  of  Manly,  fresh-looking  till  containing 
limestone  and  other  pebbles  was  thrown  out  in  digging  a  ditch. 
This  may  be  the  lowan. 

CERRO  GORDO  COUNTY. 

In  the  western  part  of  the  lowan  area,  at  several  places  on 
the  gently  undulating,  little-dissected  plains  of  Cerro  Gordo 
county,  the  auger  penetrated  very  dense,  noncalcareous  clay,  in 
most  cases  gray  or  drab  colored,  in  some  cases  brownish.  This 
clay  contains  few  or  no  pebbles  and  suggests  the  super-Kansan 
" gumbo."  It  is  unlike  the  ordinary  weathered  upper  part  of 
the  Kansan  till  or  of  the  lowan  till.  In  places  this  grades  down 
into  clay  which  is  of  similar  color  and  texture  but  is  calcareous 
and  contains  limestone  and  other  pebbles,  which  indicates  that 
it  is  till.  It  might  be  that  the  character  of  the  clay  here  is  due 
to  the  incorporation  of  much  material  from  the  underlying 
Lime  Creek  shale. 

FRANKLIN  COUNTY. 

Several  miles  southeast  of  Hampton  there  is  a  loess-mantled, 
bulky  ridge  between  Squaw  and  Haynes  creeks.  This  may  be  a 
remnant  of  an  old  divide  on  the  Kansan  drift  plain.  A  cut  and 
boring  near  the  crest  of  the  ridge  (Geneva  township,  Township 
91  North,  Range  19  West,  section  7,  northwest  quarter)  (at 
1200  ±  feet  above  sea  level)  showed : 


GUMBO  IN  TAMA  COUNTY  105 

DRIFT  SOUTHEAST  OF  HAMPTON,  IOWA. 

Feet. 

Soil  1 

Till   (lowan?),  loose,  yellow,  leached 2 

Clay,  "gumbo"-like,  lense,  dark  brown,  sticky,  noncalcareous  and 

with  coarse  sand  grains  or  small  pebbles  in  lower  part 6 

Dark  brown  sandy  material   (decayed  limestone?) 1 

Limestone. 

Two  miles  southwest  of  Faulkner  (Osceola  township,  Town- 
ship 90  North,  Eange  19  West,  near  southwest  corner  of  sec- 
tion 17)  three  feet  of  dense,  gray,  noncalcareous  "gumbo"  is 
exposed  in  the  slope  beside  the  schoolhouse  (1140  ±  feet  above 
sea  level)  below  thin  pebbly  till.  This  is  near  the  foot  of  the 
slope  which  marks  the  margin  of  the  Wisconsin  drift.  It  is 
thus  impossible  to  say  whether  the  thin  pebbly  till  above  the 
' '  gumbo ' '  is  lowan  or  Wisconsin. 

TAMA  COUNTY. 

There  are  several  exposures  of  " gumbo"  in  Tama  county, 
but  the  interpretation  to  be  placed  upon  them  is,  at  present, 
somewhat  problematical.  The  exposures  are  in  tracts  where 
much  dissection  has  occurred  so  that  it  is  possible  the  overlying 
till,  where  such  is  present,  may  be  Kansan  instead  of  lowan  till. 
At  one  exposure  there  is  no  overlying  till  and  the  "gumbo"  may 
be  regarded  as  super-Kansan. 

About  four  miles  northwest  of  Toledo,  near  the  middle  of  the 
east  half  of  section  7  (Township  83  North,  Eange  15  West), 
gray,  noncalcareous  "gumbo,"  spotted  with  red  at  the  top,  out- 
crops beneath  the  loess,  in  the  west-facing  slope,  about  twenty- 
five  feet  below  the  top.  Beneath  is  leached,  brown  till  (Kan- 
san?). Between  two  and  three  miles  northeast  of  Gladstone 
(Otter  Creek  township,  Township  83  North,  Eange  14  West, 
line  section  22)  the  Chicago,  Milwaukee  &  St.  Paul  railway  cut 
just  east  of  the  viaducts  affords  an  interesting  exposure  of  the 
following  deposits  (figure  7) : 

DRIFT  NORTHEAST  OF  GLADSTONE,  IOWA. 

Feet. 
4.     Loess,  buff,  leached  for  four  feet,  gray  in  lower  part  where 

thickest  and  contains  CaCO3  concretions 5-10 

3.  Upper  till,  oxidized  brownish  in  upper  part  and  with  dis- 
tinct pebble  band  at  top,  leached  for  three  feet,  highly  cal- 
careous below,  with  CaCOs  concretions 3-6 


106  THE   IOWAN   DRIFT 

2.  Clay,  "gumbo,"  dense,  gray,  noncalcareous  and  containing 
scattered  small  pebbles.  Upper  surface  uneven  as  though 
eroded  or  disturbed  by  the  overriding  ice 3-6 

1.  Lower  till,  oxidized  brownish  for  ten  feet  ±,  highly  cal- 
careous to  base  of  "gumbo."  This  grades  downward  into 
gray  to  dark  slate-colored  till  full  of  CaCO3  concretions; 
exposed  15 


of   drift   exposed    in    Chicago,    Milwaukee   &   St.    Paul    railway   cut 
northeast  of  Gladstone,  Iowa. 

There  is  gradation  between  No.  1  and  No.  2.  Numbers  2 
and  3  were  cut  away  at  both  sides  by  erosion  prior  to  the  deposi- 
tion of  the  loess.  The  latter  mantles  the  crest  and  slopes  of  this 
spur  of  the  upland.  Estimates  of  pebbles  from  the  upper  and 
the  lower  tills  show  no  marked  difference  in  lithology. 

About  a  mile  northeast  of  this  place  (in  Otter  Creek  town- 
ship, section  11,  near  the  southeast  corner)  dense,  dark  gray 
gumbo,  mottled  with  red  in  the  upper  part,  was  seen  exposed 
beneath  five  to  ten  feet  of  loess  and  still  farther  northeast  a 
road  cut  just  south  of  the  middle  of  section  1  exposed  the  fol- 
lowing : 

DRIFT  NORTHWEST  OF  Vixixo,  IOWA. 

Feet. 

Loess     : 5-6 

"Gumbo,"  dense,  brownish  gray,  tough  and  noncalcareous 5 

Till  (Kansan?),  brown,  leached,  exposed  in  slope 7 

Between  four  and  five  miles  north  of  the  railroad  cut  and  about 
three  miles  northwest  of  the  exposure  last  noted  above  (in  a 
slope  one-fourth  mile  south  of  the  schoolhouse  on  the  east  line 
of  section  33,  Carroll  township,  Township  84  North,  Range  14 
West)  gray  gumbo  was  exposed  twenty-five  to  thirty  feet  above 
the  bottom  of  the  till  slope.  This  has  a  thickness  of  at  least  five 
feet,  as  was  determined  by  boring ;  it  appears  to  grade  into  the 
till  below  and  is  overlain  by  thin  brownish  till.  At  levels  six 
and  ten  feet  higher  up  the  gumbo  is  slightly  exposed  in  patches 


GUMBO  IN  TAMA  COUNTY  107 

surrounded  by  till  as  though  it  outcrops  through  holes   in   an 
overlapping  thin  mantle  of  till. 

Some  of  the  other  cuts  in  Carroll  and  Otter  Creek  townships 
show  a  distinct  reddish  brown  ferretto  at  the  top  of  the  till  and 
beneath  the  loess.  At  these  places  and  at  those  where  the  top 
of  the  till  is  less  highly  oxidized,  the  " gumbo"  and  upper  till 
are  not  seen,  evidently  because  of  their  removal  prior  to  the 
deposition  of  the  loess.  These  exposures  in  Tama  county  are 
in  a  belt  of  country  five  to  twelve  miles  wide  which  lies  north  of 
Iowa  river  valley  and  west  of  Salt  creek  valley,  and  in  which 
a  notable  amount  of  erosion  was  accomplished  prior  to  the 
deposition  of  the  loess.  Most  of  this  area  has  been  mapped  as 
outside  the  limit  of  the  lowan  drift  and  there  is  good  reason 
for  regarding  it  as  such.  The  presence,  however,  of  an  upper 
till  overlying  the  gumbo  in  the  exposures  in  Otter  Creek  and 
southern  Carroll  townships  raises  the  question  whether  the 
lowan  ice  may  not  have  extended  as  far  south  as  Iowa  river 
valley.  Is  the  succession  to  be  regarded  as : 

Loess 

Till  (lowan) 

"Gumbo" 

Till  (Kansan) 
or,  as  in  Carroll  county: 

Loess 

Till  (Kansan) 

"Gumbo" 

Till  (pre-Kansan) 

The  same  question  is  raised  by  conditions  observed  about 
twelve  miles  farther  north.  Seven  or  eight  miles  west  of  Traer 
(Grant  township,  Township  86  North,  Eange  15  West,  section 
33,  near  middle  of  south  line)  a  road  cut  on  the  steep  slope  of 
a  ravine  tributary  to  Four-Mile  creek  exposed  the  following, 
when  seen  in  September,  1915 : 

DRIFT  WEST  OF  TRAER,  IOWA. 

Feet. 

6.     Loess,  buff  to  grayish 

5.     Till,  rusty  brown  and  very  stony  at  top 5-10 

4.     "Gumbo,"  dense,  sticky,  gray,  noncalcareous  clay 4 


108  THE   IOWAN   DRIFT 

3.     Till,  gray,  crumbly  and  full  of  arkosic  material  as  from 

disintegrated  granite    2 

2.     Till,  brown,  leached 4 

1.     Till,  brown,  highly  calcareous. 

There  is  gradation  from  No.  1  to  No.  2,  from  No.  2  to  No. 
3  and  from  No.  3  to  No.  4.  A  boring  sunk  through  the  lower 
four  feet  of  No.  5  into  No.  4  showed  that  the  "'gumbo"  really 
extends  back  into  the  hill  beneath  the  upper  till.  Between  two 
and  three  miles  farther  east  on  the  north  side  of  Wolf  creek 
valley  there  is,  beneath  ten  feet  of  loess,  a  dark  ferretto  at  the 
top  of  the  leached  till.  A  little  lower  down  the  valley  gumbo 
is  exposed  but  it  appears  not  to  extend  into  the  hill.  At  one 
place  the  gumbo  itself  is  red.  Unfortunately  there  was  insuffi- 
cient time,  when  this  exposure  was  found,  to  determine  what 
were  the  real  relations,  as  they  were  not  clearly  shown  in  the  cut. 
The  country  bordering  Wolf  and  Four-Mile  creeks  west  of 
Traer  has  a  maturely  dissected  topography  with  seventy  to 
one  hundred  feet  of  relief,  in  contrast  with  the  little-eroded, 
gently  undulating  topography  immediately  to  the  north  and 
south,  so  that  there  is  the  same  question  as  to  whether  the  suc- 
cession is: 

Loess 

Till  (lowan) 

"Gumbo" 

Till  (Kansan) 
or: 

Loess 

Till  (Kansan) 

"Gumbo" 

Till  (pre-Kansan) 

The  question  concerning  the  interpretation  of  the  age  of  the 
deposits  in  these  Tama  county  exposures  arises  from  the  fact 
of  their  occurring  in  tracts  where  the  amount  of  erosion  which 
has  been  accomplished  since  the  deposition  of  the  upper  till  is 
considerably  more  than  that  generally  seen  in  the  lowan  area 
and  about  the  same  as  that  in  the  Kansan  area  south  of  Iowa 
river.  Further,  in  several  new  cuts  along  the  line  of  the  Chi- 
cago, Milwaukee  &  St.  Paul  Eailway  west  of  the  area  of  the  Des 
Moines  lobe  in  southern  Carroll  county  and  southeastern  Craw- 


GUMBO  IN  TAMA  COUNTY  109 

ford  county,  a  well  developed  bed  of  similar  dense,  gray,  non- 
calcareous  "gumbo"  lies  between  two  highly  calcareous  till 
sheets.  Here  the  general  relations  and  the  large  amount  of 
erosion  which  has  been  accomplished  since  the  deposition  of  the 
upper  till  indicate  that  the  latter  is  of  Kansan  age.  If  this  be 
correct,  there  is  clearly  a  pre-Kansan  (or  super-Nebraskan) 
" gumbo"  as  well  as  a  super-Kansan  "gumbo."9"  As  indicated 
above,  the  relations  are  much  the  same  in  Tama  county,  so  that, 
for  the  present  at  least,  final  judgment  as  to  these  latter  ex- 
posures must  be  suspended. 

The  question  may  be  asked,  "If  there  is  evidence  of  a  pre- 
Kansan  bed  of  "gumbo"  why  may  not  the  "gumbo"  at  all  the 
exposures  cited  above  be  of  pre-Kansan  age  and  the  overlying 
till  in  the  lowan  area  be  Kansan?"  In  answer  to  this  it  may 
be  said  that  the  wide  distribution  of  "gumbo"  on  top  of  the 
Kansan  drift  in  southern  Iowa  and  its  general  absence  from 
the  surface  of  the  uppermost  till  in  the  lowan  area,  excepting 
near  Mitchell,  makes  it  much  more  probable  that,  the  upper  till 
in  the  lowan  area  is  post-Kansan  and  that  the  underlying 
"gumbo"  is  super-Kansan.  Then  too  the  moderate  amount  of 
modification  by  weathering  and  the  small  amount  of  erosion  of 
the  uppermost  till  of  the  lowan  area,  taken  as  a  whole,  seems  to 
the  writers  evidence  that  the  latter  till  is  younger  than  Kansan. 
The  different  lines  of  evidence  support  each  other. 

While  it  may  be  necessary  to  withhold  judgment  concerning 
some  of  the  occurrences  cited  above,  it  seems  to  the  writers  that 
there  remains  a  body  of  definite  evidence  indicating  that  there 
really  is  a  distinct  super-Kansan  "gumbo"  and  a  post-Kansan 
drift  in  the  lowan  area. 

9«Kay,  G.  F.,  Pleistocene  deposits  between  Manilla  in  Crawford  County  and  Coon 
RapiJs  in  Carroll  County:  Iowa  Geological  Survey,  Vol.  XXVI,  pp.  213-231. 


110  THE   IOWAN   DRIFT 

CHAPTER  IV 

OTHER  EVIDENCES  OF  POST-KANSAN  GLACIATION. 
General  Character 

Besides  the  lines  of  evidence  which  already  have  been  present- 
ed and  those  which  are  to  follow,  certain  phenomena  have  been 
noted  which,  though  susceptible  of  various  interpretations  and 
not  conclusive  in  themselves,  are,  in  a  way,  corroborative  and 
lend  support  to  the  foregoing  conclusion.  These  include  de- 
scriptions of  some  exposures  of  lowan  drift  and  logs  of  wells 
taken  from  the  reports  of  the  Iowa  Geological  Survey  and  from 
W  J  McGee's  paper  on  northeastern  Iowa,  which  may  be  pre- 
sented together  in  this  chapter. 

In  the  course  of  the  present  investigation  an  effort  was  made 
to  examine  most  of  the  exposures  to  which  definite  reference 
had  been  made  in  the  published  papers  as  showing  lowan  till 
distinguishable  from  older  deposits.  Some  of  the  old  exposures 
are  now  so  badly  slumped  and  overgrown  that  no  accurate  de- 
termination of  the  deposits  can  be  made.  Most  of  those  seen 
were  unsatisfactory.  Some  of  the  old  exposures  and  some  of 
the  new  ones  are  suggestive.  Taken  by  themselves  most  of  them 
are  of  very  slight  value  as  evidence  of  post-Kansan  glaciation. 
A  few,  such  as  the  cut  in  Johnson  county,  are  important.  They 
embrace  occurrences  of  till  over  silt  or  loess;  of  two  tills  with 
an  intervening  soil;  till  over  weathered  gravel;  till  over  more 
weathered  till ;  till  with  apparent  intermixture  of  older  ' '  gumbo ' ' 
or  other  deposits. 

For  readiness  of  reference,  these  are  presented  somewhat  in 
detail  in  the  form  of  notes. 

Notes  on  certain  other  supposed  occurrences  of  lowan  drift 
may  be  found  in  Appendix  C. 

WINNESHIEK    COUNTY. 

A  boring  at  a  point  about  five  miles  southwest  of  Ridgeway  (in 
Sumner  township,  Township  88  North,  Eange  10  West,  section 
4,  west  line  of  the  northwest  quarter),  showed  the  following: 


POST-KANSAN  TILL  IN  CHICKASAW  COUNTY  111 

DBIFT  SOUTHWEST  OF  RIDGEWAY,  IOWA. 

Feet. 
3.     Till   (lowan?),  yellow,  leached 3 

2.  Silt,  loesslike,  grayish,  leached 3 

1.  Till  (Kansan?),  leached  for  one  foot,  calcareous  helow. 

HOWARD  COUNTY. 

Professor  Calvin10  described  the  section  exposed  in  a  cut  on 
the  Chicago  Great  Western  railway  south  of  Elma,  as  follows : 

A  deep  railway  cut  one  and  a  half  miles  south  of  Elma  re- 
veals the  Kansan  drift  in  its  unweathered  phase.  A  few  rods 
north  of  a  wagon  bridge  which  here  spans  the  cut,  the  section 
shows : 

Feet. 

3.  Yellow,  unweathered  lowan  till 6 

2.  Old  peaty  soil  developed  in  the  intervals  between  the  Kansan 
and  the  lowan  stages  of  glaciation 2 

1.     Blue  unweathered  Kansan  to  bottom  of  the  cut 15 

There  is  here  no  f erretto  zone  at  the  surface  of  the  Kansan ; 
the  organic  material  of  the  peaty  soil  bed  was  capable  of  more 
than  counter-balancing  any  effects  of  oxidation  which  might 
have  taken  place  before  the  Kansan  surface  was  covered  and 
protected  from  further  change  bv  the  deposition  of  the  lowan 
drift. 

CHICKASAW  COUNTY. 

In  July,  1907,  R.  T.  Chamberlin  examined  the  cuts  southeast 
of  New  Hampton  on  the  Chicago  Great  Western  railway.  At 
the  gravel  pit  one-fourth  mile  southeast  of  the  station,  over- 
lying ten  feet  of  rusty  red-brown  sand  and  gravel  at  the  south 
end  of  the  exposure,  he  found  "  nearly  two  feet  of  a  yellow- 
brown,  non-calcareous  drift,  presumably  lowan,  since  there  are 
lowan  bowlders  on  the  surface  of  the  hillside."  The  following 
also  is  from  his  notes : 

Half  a  mile  from  the  station  at  the  overhead  bridge  is  a  cut 
nearly  20  feet  deep  where  the  steam  shovel  has  been  within  a 
year  or  two.  This  cut  is  through  a  ridge  so  that  the  level  of  the 
tracks  is  slightly  higher  than  the  top  of  the  gravel  in  the  pits 
just  mentioned  (Top  of  both  gravels  appear  same  height).  The 
section  here  is: 

Feet. 

1.  lowan  drift    4-8 

2.  Buchanan    [gravel],    interglacial 1-4 

3.  Kansan,  brown  above,  but  chiefly  bluish  till 6-7 

4.  Aftonian   sands   and   gravels,  upper   eight  inches   cemented 
with  CaCOs.     Below  this  non-consolidated  and  easily  dug. 
Upper   part  at   about  the   level   of  the   tracks.     Thickness 

by  digging  a  little  into  the  talus 3 


10Iowa  Geological   Survey,  Vol.  XIII,  p.   63. 


112  THE   IOWAN   DRIFT 

The  bottom  of  the  ditch  is  here  several  feet  below  the  level 
of  the  tracks.  The  lowan  is  here  noncalcareous,  yellow  brown, 
and  stands  well  as  a  cliff  face.  The  Buchanan  is  very  variable. 
In  some  places  there  is  a  distinct  soil  line  at  its  top.  Through- 
out most  of  the  cut  it  contains  layers  of  clean  yellow  sand  and 
generally  free  from  pebbles.  In  some  places  this  is  very  soft; 
elsewhere  it  has  been  cemented  into  a  true  sand  stone.  Inter- 
bedded  in  some  places  are  clayey  layers.  Where  the  Kansan 
and  Aftonian  are  best  exposed  the  Buchanan  loses  its  chief 
characteristics,  being  represented  here  by  altered  streaky  sandy 
and  clayey  till. 

The  upper  portion  of  the  Kansan  becomes  brownish  but  the 
greater  part  is  bluish.  It  is  calcareous  throughout.  The 
Aftonian  resembles  that  at  Afton  Junction  closely.  • 

See  tables  (Appendix  A)  for  estimates  of  pebbles  from  these 
various  deposits. 

The  cuts  were  examined  in  1914  by  the  present  writers.  At 
the  gravel  pit  Mr.  Leighton  found : 

DRIFT  SOUTHEAST  OF  NEW  HAMPTON",  IOWA. 

Feet. 

Clay,  yellow,  with  occasional  pebbles -. 2 

Gravel    and    sand,    yellowish    brown    to    reddish    brown,    cross- 
.  bedded,   leached   of  all   calcareous  material,   granites,   green- 
stone and  dolerites  much  decomposed.  Clay  ironstones  present  20 

The  railroad  cut  at  the  viaduct  was  too  badly  obscured  by 
vegetation  and  slumping  for  accurate  determination  except  in 
the  upper  part. 

BUCHANAN  COUNTY. 

An  exposure  frequently  mentioned  in  connection  with  discus- 
sions of  the  lowan  drift  is  the  old  gravel  pit  near  Doris  on  the 
Illinois  Central  railroad,  about  four  miles  east  of  Independence 
(Byron  township,  Township  89  North,  Eange  8  West,  section 
32,  northwest  quarter).  This  was  Doctor  Calvin's  type  exposure 
of  Buchanan  gravel,  if  not  also  of  lowan  till.  The  exposure 
is  almost  wholly  obscured  by  slumping  and  vegetation.  Trees 
up  to  eight  inches  in  diameter  have  grown  in  the  bottom  of  the 
excavation  and  the  banks  are  mostly  grassed.  On  the  north  side, 
when  the  pit  was  visited  by  the  present  writers  in  1914,  there 
had  been  some  recent  excavation  for  road  gravel  so  that  the 
upper  till  and  the  underlying  gravel  were  well  exposed  through 


POST-KANSAN   TILL  IN   BUCHANAN  COUNTY  113 

a  space  about  fifty  yards  in  extent.  The  following  was  seen 
below  the  level  of  the  gently  undulating  bowlder-strewn  lowan 
plain : 

DRIFT  AT  ILLINOIS  CENTRAL  RAILROAD  GRAVEL  FIT,  DORIS,  IOWA. 

Feet. 

3.     Soil,  dark i/24 

2.     Till,    dense,    hard,   jointed    and    leached,    dull   yellowish, 

pebbly.     No  limestone  pebbles  seen 3     -6 

1.  Gravel,  rusty  brown,  ferruginous,  pebbles  small  to  eight 
inches  in  diameter,  largely  of  polished  quartz  and  chert 
with  some  disintegrating  granites 3 

In  two  places  stringers  of  gravel  run  up  into  the  till  and  in 
one  place  the  till  extends  down  one  and  one-half  feet  into  a  de- 
pression in  the  gravel.  The  deposit  overlying  the  gravel  is 
clearly  glacial  till  and  the  only  question  is  that  of  its  age.  The 
gravel  as  originally  exposed  is  reported  to  extend  down  to  a 
depth  of  twenty  feet  below  the  base  of  the  upper  till  and  to  be 
underlain  by  dense  bluish  till. 

In  September,  1907,  this  pit  was  visited  by  T.  C.  and  R.  T. 
Chamberlin.  The  following  is  from  the  notes  of  the  latter : 

From  Independence  we  drove  east  to  see  the  famous  cut  along 
the  I.  C.  R.  R.  tracks  three  miles  east  of  the  town.  This  is  the 
type  locality  for  the  lowan  drift.  On  the  way  out  there  we  saw 
sloughs  and  slight  hummocky  bunches  which  cause  a  slight  un- 
evenness  in  the  regular  slopes.  The  topography  looks  young — 
almost  Wisconsin  in  places. 

The  cut  is  just  west  of  Doris  station  and  has  been  used  ex- 
tensively for  gravel.  The  pit  shows  Buchanan  gravels  capped 
by  0-6  feet  of  a  fresher  appearing  yellowish  till  which  closely 
resembles  the  upper  yellow  till  at  Oelwein.  It  is  a  brighter 
colored  material  than  is  usual  in  the  oxidized  part  of  the 
Kansan,  but  it  contains  more  Fe203  apparently  for  the 
shades  are  deeper  than  the  yellow  gray  Kansan  upper  zone. 
The  upper  part  is  non-calcareous  as  is  the  till  at  Oelwein,  but 
the  lower  portion  is  calcareous.  Leaching  has  gone  down  about 
4  feet. 

Below  this  till  are  the  Buchanan  gravels  which  is  the  material 
sought  for  the  railroad.  They  are  considerably  oxidized  but 
contain  inclusions  of  till.  Fifty  pebbles  dug  from  the  lowan 
drift  at  this  gravel  pit  were  classified.  (See  Table  No.  Ill, 
Appendix  A.) 

The  striking  feature  of  this  set  of  pebbles  is  the  old  and 
weathered  condition  of  the  igneous  rocks  and  the  great  propor- 


114  THE  IOWAN   DRIFT 

tion  of  polished  quartz  and  chert  pebbles.  The  granites  were 
crumbly  while  the  greenstones  generally  were  incased  in  thick 
weathered  zones.  The  mica  schist  was  very  rotten. 

The  highly  polished  quartz  and  chert  pebbles  were  of  the 
type  usually  assigned  to  pre-glacial  deposits.  They  may  have 
been  subject  to  wind  polishing  while  resting  upon  the  surface 
of  the  older  drift,  while  the  lowan  glacier  was  advancing.  How- 
ever, some  of  the  other  quartz  pebbles  were  sub-angular  and  not 
polished  at  all  though  they  might  have  been  buried  beneath  the 
surface. 

On  the  whole  it  looks  as  though  the  lowan  ice  had  merely 
scraped  up  the  surface  portion  of  the  older  drift  and  that  these 
old  and  weathered  pebbles  received  most  of  their  weathering 
before  incorporated  in  the  lowan  drift. 

The  idea  of  the  lowan  being  "calcareous  to  the  grass  roots" 
is  not  supported  at  Independence  nor  at  any  other  point  where 
I  have  seen  this  drift.  Its  darker  color  compared  with  the  fresh 
yellow  Kansan  may  be  due  to  the  fact  that  some  of  the  oxidized 
ferretto  material  has  been  mixed  with  scrapings  of  the  yellow 
till.  The  Buchanan  gravels  below  looked  older  than  the  lowan. 

The  relations  of  the  lowan  till  to  the  older  deposits  are  il- 
lustrated by  the  following  cited  by  Doctor  Calvin11 : 

A  very  common  relation  of  Pleistocene  deposits  is  illustrated 
by  the  well  section  on  land  of  J.  W.  Welch,  in  the  southwest  quar- 
ter of  section  28,  Buffalo  township.  The  record  shows, 

Feet. 
3.     Dark  soil  and  yellow  till 4 

2.  Reddish  ferruginous  sand  and  gravel 23 

1.  Blue   clay,   penetrated 1 

No.  1  of  this  section  is  Kansan  drift,  No.  2  is  Buchanan  gravel, 
and  No.  3  is  lowan  till.  In  the  same  quarter  section  another 
well  shows: 

Feet. 

3.  Soil  and  yellow  till   22 

2.  Reddish   gravel    _ 11 

1.     Blue  clay,  with  pockets  of  sand 19 

Concerning  the  relations  at  the  Doris  gravel  pit  Doctor  Calvin 
wrote12 : 

The  gravel  rests  on  typical  Kansan  blue  clay  and  is  overlain 
by  yellow  lowan  till  which  varies  from  less  than  a  foot  in  thick- 
ness at  the  western  end  of  the  exposure  to  more  than  six  feet  at 
the  extreme  eastern  end.  Two  facts  are  at  once  apparent ;  first, 

I1lowa  Geoloeical   Survey,  Vol.  VIII,  pp.   239-240,   1897. 
12Op.  cit.,  p.  242. 


POST-KANSAN  TILL  IN  LINN  COUNTY  115 

the  gravel  is  interglacial  in  position;  second,  it  is  very  old  as 
compared  with  the  overlying  lowan  till. 

LINN  COUNTY. 

Cuts  along  the  newly  graded  line  of  the  Waterloo,  Cedar 
Falls  &  Northern  electric  railway  afforded  numerous  clean  ex- 
posures of  the  upper  part  of  the  drift.  In  one  of  these,  north- 
west of  Marion  (Monroe  township,  Township  84  North,  Range  8 
West,  section  4,  southwest  quarter),  there  is  a  suggestion  of 
overriding  by  a  readvance  of  the  ice.  There  seems  to  be  a  mix- 
ture of  leached  and  calcareous  till.  The  till  (lowan  *)  at  A  (fig- 
ure 8). is  highly  calcareous  below  a  leached  zone  three  feet  in 


Road 
Till  \  /        [       <^r>ri          J    I    ?,anH    /     <*B.-'~       <"        ?7umbo 

Fig.  8. — Diagram  of  cut  on  Waterloo,  Cedar  Palls  &  Northern  Electric  railway,  north- 
west of  Marion,  Iowa,  showing  relations  of  lowan  (t)  till  to  dune  sand 
(B  B)  and  "gumbo"  (C)  super-Kansan?. 

thickness.  At  B.  B.  are  two  pockets  of  fine  sand  with  dimensions 
of  six  by  ten  feet,  which  resembles  dune  sand,  and  at  O  is  dense, 
noncalcareous,  gray  clay  with  small  pebbles.  This  resembles 
the  super-Kansan  ".gumbo."  While  the  deposits  suggest  over- 
riding by  a  readvance  of  the  ice,  the  relations  are  not  sufficiently 
clear  to  make  sure  that  there  is  more  than  one  till  sheet.  So 
also  with  the  next  cut  in  the  northwest  quarter  of  section  4, 
which  shows: 

DRIFT  ox  WATERLOO,   CEDAR  FALLS  &  NORTHERN   RAILWAY,   NORTH- 
WEST OF  MARION,  IOWA. 

Feet. 

7.     Loam,  sandy   1-2 

6.     Gravel,  rusty,  in  layers  and  pockets 0-2 

5.     Till   (lowan?),  brown,  leached 2-3 

4.     Till    (lowan?),  brown,  calcareous 2-3 

3.     Sand     1-2 

2.     Clay,  brown  to  gray,  partly  leached,  partly  calcareous ....   1-3 

This  grades  down  into 

1.  Clay  (Kansan?),  dense,  dark,  slate-colored,  pebbly  till, 
In  one  place  below  a  black  strip,  possibly  a  remnant  of 
an  old  soil,  this  clay  is  greenish  and  calcareous 1± 

There  is  more  or  less  mixing  and  the  relations  are  not  so  clear 
and  simple  as  the  above  might  seem  to  indicate. 

And  again  at  the  viaduct  in  Otter  Creek  township  (Township 
85  North,  Range  7  West,  section  29,  northeast  quarter)  is  the 
following : 


116  THE   IOWAN   DRIFT 

DRIFT    ON    WATERLOO,    CEDAR    FALLS    &    NORTHERN    RAILWAY,    Six 
MILES  SOUTHEAST  OF  CENTER  POINT,  IOWA. 

Feet. 

4.     Dune  sand,  stratified 5-12 

3.     Till   (lowan?),  light  buff,  pebbly,  leached 3 

2.     Till,  similar  to  above    (lowan?),  calcareous 1 

1.     Till    (Kansan),  dense,  brown,  calcareous,  of  different  tex- 
ture from  No.  2  and  with  a  fairly  distinct  line  of  division  0-  4 

On  the  washed  surface  of  the  lower  till  (No.  1)  are  small, 
brown,  pebble-like  masses  of  clay  one-fourth  to  one  half  incji 
long  which  can  be  crushed  with  the  fingers.  They  suggest  "buck- 
shot" or  ferruginous  concretions  seen  in  some  of  the  glacial 
clays.  They  are  not  seen  in  the  upper  till,  Nos.  2  and  3. 

JONES   COUNTY. 

The  large  cut  on  the  Chicago,  Milwaukee  &  St.  Paul  railway 
about  two  miles  east  of  Martelle,  (Greenfield  township,  Town- 
ship 83  North,  Range  4  West,  section  9)  affords  the  interesting 
exposure  illustrated  in  figure  9. 


Fig.  9.— Diagram  of  cut  on  Chicago.  Milwaukee  &  St.  Paul  railway  east  of  Martelle, 
Iowa,  showing  relations  of  Kansan  till  (1  and  2)  ;  gray  clay  (3)  ;  Buchanan 
(?)  gravel  (4)  ;  lowan  (?)  till  (5)  ;  loess  (6). 


The  generalized  section  is  as  follows : 


DKIHT  ON  CHICAGO,  MILWAUKEE  &  ST.   PAUL  RAILWAY,   Two  MILES 
EAST  OF  MARTELLE,  IOWA. 

Feet. 

6.     Clay  (loess),  pebbleless,  thicker  in  sag  than  over  the  swells  1-  5 
5.     Till  (lowan?),  lens-shaped  bed,  buff  to  gray,  leached,  pebbly  0-  5 

4.     Sand,  buff  to  brown,  over  rusty  gravel  (Buchanan?) 0-10 

3.  In  a  buried  sag  which  the  cut  crosses  obliquely  is  gray 
clay,  noncalcareous  and  not  well  bedded  in  the  upper  part 
("gumbo"-like),  and  laminated  and  calcareous  below 

(Yarmouth?)     0-  8 

2.     Till    (Kansan),   buff,   leached   3-5   feet,   calcareous   below; 

exposed    1-15 

1.  Till  (Kansan),  calcareous,  gray  on  dry  face,  dark  slate- 
colored  where  moist;  exposed  _ 1-10 

In  places  at  the  top  of  No.  2  is  a  limy  crust  or  a  line  of  con- 
cretions composed  of  the  calcium  carbonate  leached  from  No.  3. 
The  thin  upper  bed  of  till  (No.  5)  suggests  a  readvance  of  the 
ice  after  the  deposition  and  weathering  of  the  sand  and  gravel 
and  the  correlations  indicated  may  perhaps  be  made. 


POST-KANSAN  TILL  IN  JOHNSON  COUNTY  117 

Professor  Calvin13  gives  the  following  log  of  a  well  bored  on 
the  gently  undulating  plain  at  a  point  three  or  four  miles  north 
of  Martelle  (Fairview  township,  Township  84  North,  Eange 
4  West,  section  20,  near  center).  The  log  is  said  to  be  typical 
of  a  very  large  number  of  wells  in  this  county. 

Loo  OF  WEIX  ONE-HALF  MILE  SOUTHWEST  OF  FAIRVIEW,  IOWA. 

Feet. 

5.    Loam  or  vegetable  mould,  black 1 

4.    day,    yellow,    of    lowan    stage 8 

3.     Dark  brownish  band,  upper  portion  of  Kansan  stage 4 

2.     Blue  unoxidized  portion  of  Kansan  stage 12 

1.     Sand  in  which  occurs  an  abundance  of  water 4 

JOHNSON  COUNTY. 

One  of  the  most  significant  exposures  seen  was  the  first  cut 
north  of  Iowa  river  on  the  electric  railroad  about  thirteen  miles 
northwest  of  Iowa  City  (Jefferson  township,  Township  81  North, 
Eange  7  West,  section  2,  southeast  quarter).  This  was  ex- 
amined by  Mr.  Alden  in  1905,  and  in  1912, 1913  and  1914  by  Mr. 
Leighton  who  has  published  views  and  a  description  of  the  ex- 
posure14. The  cut  is  in  the  lower  slope  seventy  or  eighty  feet 
below  the  highest  part  of  the  ridge  to  the  north  and  its  base  is 
not  over  thirty  feet  above  the  river. 


Fig.  10.— Diagram  of  cut  on  electric  railway  near  Iowa  river,  northwest  of  Iowa 
City,  Iowa,  showing  relations  of  Kansan  till  (1,  2  and  2a)  ;  Buchanan 
gravel  (3)  ;  lowan  till  (4)  ;  loess  (5). 

Rising  above  the  track  level  to  a  maximum  height  of  about 
twelve  feet  (figure  10  and  Plate  VII)  is  dense,  dark  blue,  cal- 
careous till  (No.  1)  (Kansan).  This  grades  upward  into  buff 
to  rusty  brown,  oxidized,  partly  leached  till  (Kansan)  (No.  2) 
from  nothing  to  ten  feet  thick.  Overlying  this  is  a  bed  of  rusty 
brown  gravel  (Buchanan)  (No.  3)  which  is  partly  cemented  by 
iron  oxide  and  in  which  the  crystalline  pebbles,  which  range  in 

"Iowa  Geological  Survey,  Vol.  V,  p.  65,  1895. 

14Leighton,  M.  M.,  An  exposure  showing  post-Kansan  glaciation  near  Iowa  City, 
Iowa:  Jour.  Geology,  Vol.  21,  pp.  431-435,  1913.  The  Pleistocene  history  of  Iowa 
river  valley,  north  and  west  of  Iowa  City  in  Johnson  County:  Iowa  Geologica" 
Survey,  Vol.  XXV,  (1914)  pp.  142-146,  1916. 


118  THE   IOWAX   DRIFT 

size  up  to  one  foot  in  diameter  but  are  mostly  less  than  three 
inches,  are  much  decayed.  The  gravel  bed  is  contorted  and 
folded  as  if  by  pressure  from  the  northwest.  One  of  the 
synclinal  folds  is  seven  feet  deep.  Overlying  the  gravel  is  yel- 
lowish, blue-streaked  till  (lowan)  (No.  4)  two  to  four  feet  thick 
across  the  summit  and  attaining  a  thickness  of  at  least  eight  feet 
along  the  west  monoclinal  limb.  This  till  is  highly  calcareous 
excepting  in  the  upper  few  feet  where  it  is  leached.  Yellow 
fossiliferous  loess  (No.  5)  lies  on  the  northwest  slope  and  loess 
and  sand  occur  on  the  southeast  or  riverward  slope. 

This  cut  was  reexamined  by  Mr.  Alden  in  June,  1915,  and 
again  in  September,  the  last  time  in  company  with  R.  D.  Salis- 
bury, Frank  Leverett,  and  George  F.  Kay.  Beneath  the  south- 
east slope  of  the  hill,  in  the  lower  end  of  the  cut  the  relations  are 
not  entirely  clear  but  there  is  here,  below  the  loess,  a  thin  bed 
of  bluish  gray  clay  (No.  2a)  similar  to  the  super-Kansan 
" gumbo."  This  rises  westward  in  the  section  on  top  of  the 
rusty  jointed  and  weathered  lower  till  (No.  2).  Just  below  the 
trees,  this  is  covered  by  only  three  feet  of  loess  and  soil.  Im- 
mediately west  of  the  trees  (A)  the  crumpled  bed  of  gravel 
shown  in  Plate  VII  comes  in  and  the  "gumbo"  clay  disappears. 
The  crumpled  condition  of  the  weathered  gravel  bed  and  the 
presence  of  the  overlying  fresher  till  appears  to  be  good  evi- 
dence of  a  post-Kansan  readvance  of  the  ice  at  this  place.  The 
upper  till,  gravel,  and  lower  till  were  carefully  examined  and 
pebbles  collected  from  each.  Secondary  constituents,  such  as 
clay  ironstones  and  calcium  carbonate  concretions  were  avoided. 
The  results  of  the  analyses  as  given  in  tables  II,  IV,  V  of  Ap- 
pendix A  show  a  higher  percentage  of  greenstones  in  the  upper 
till  but  no  marked  difference.  The  gravels  have  a  higher  per- 
centage of  granites  and  a  lower  percentage  of  limestone  and 
dolomite  than  either  till. 

Thirteen  or  fourteen  miles  southeast  of  this  place  in  the  first 
cut  west  of  the  river  on  the  electric  railroad  at  Iowa  City  (West 
Lucas  township,  Township  79  North,  Eange  6  West,  section  9), 
there  is  exposed  dense,  dark,  slate-colored  till,  regarded  by 
Doctor  Calvin  as  Kansan,  and  overlying  it  is  rusty  red  gravel 
(Buchanan)  twelve  feet  thick.  Above  the  gravel  is  twenty-five 


BOWLDERS  IN  THE  IOWAN  AREA  121 

feet  of  loess.  This  is  about  five  miles  southeast  of  what  is  re- 
garded as  the  limit  reached  by  the  lowan  ice  sheet.  The  ab- 
sence of  a  till  overlying  the  gravel  and  the  undisturbed  character 
of  the  deeply  weathered  gravel  in  this  cut  are  in  striking  con- 
trast with  the  conditions  found  in  the  cut  in  Jefferson  township 
described  above. 


CHAPTER  V 

BOWLDERS. 

Bowlders  in  the  lowan  Area 

Character  and  size — Discussions  by  former  investigators  of 
the  lowan  drift  have  given  prominence  to  the  presence  of  notably 
large  granite  bowlders  scattered  over  much  of  the  lowan  drift, 
and  these  have  been  regarded  as  particularly  characteristic  of 
the  lowan  drift. 

These  bowlders  are  dominantly  coarse-grained  granites,  either 
light  gray  or  pink,  some  so  coarse  that  the  term  pegmatite  is 
applicable.  Basic  rocks,  greenstones,  and  quartzites  are  much 
less  common  and  are  not  generally  so  large  as  the  granites. 
Among  the  latter  diameters  of  ten  to  twenty-five  feet  are  com- 
mon, and  some  measure  as  much  as  thirty-five,  forty,  or  even 
fifty  feet.  The  largest  one  known  is  in  Floyd  county,  Riverton 
township,  in  the  northwest  quarter  of  the  southwest  quarter  of 
section  22  (Plate  VIII  A).  Its  dimensions  are  fifty  by  forty  by 
eleven  and  one-half  feet  above  ground.  A  smaller  piece  which 
lies  beside  it  and  apparently  is  a  fragment  of  the  larger,  meas- 
ures seventeen  by  seven  by  one  and  one-half  feet. 

As  a  rule  the  granites  show  some  effects  of  surficial  weather- 
ing, such  as  rounding  of  their  angles  and  exfoliating  shells.  A 
few  are  badly  decomposed,  but  most  of  them  are  far  from  being 
in  an  advanced  state  of  decay.  Slight  accumulations  of  arkosic 
material  lie  in  cracks  and  cavities,  but  otherwise  most  of  the 
bowlders  are  relatively  sound. 


122 


THE   It 


I        I     I 


- 


Kansan 

ice  flow 


I  owan 
ice  flow 


Wisconsin 

(DesMoineslobe) 

ice  flow 


Glacial 
striae 


Fig.   11. — Diagram   showing   the   distribution   of   big  granite    bowlders   as    related    to 
probable  uiiec.tion.>  Oi   L.O- er  er.t  cf  ii.6  sheets  in   I3\\a. 

Geographic  Distribution — The  big  bowlders  are  most  numer- 
ous in  a  broad  belt,  or  bowlder  train,  extending  southeastward 
in  what  was  probably  the  zone  of  axial  flow  of  the  lowan  ice 
through  Mitchell,  Floyd,  Chickasaw,  southwestern  Fayette, 
Bremer,  northeastern  Black  Hawk,  Buchanan,  northeastern 
Benton,  and  Linn  counties  (figure  11).  Not  only  are  many  large 
ones  to  be  seen  here,  but  smaller  bowlders  are  numerous  also, 
and  are  being  used  for  foundations  of  buildings  and,  rarely,  are 
piled  as  stone  fences.  Many  of  the  smaller  bowlders  and  some 
large  ones  are  scattered  both  east  and  west  of  the  main  belt.  In 
the  southwestern  part  of  the  area  bowlders,  especially  large  ones, 
are  much  less  numerous.  In  this  part  one  may  travel  several 
miles  without  seeing  more  than  a  very  few  bowlders  perhaps 
two  or  three  feet  in  diameter,  and  then  suddenly  may  come 
upon  a  huge  one. 


Icwa  Geological  Survey. 


PLATE  VIII. 


A.     Large  lowan  bowlder  in  Floyd   County,  Iowa. 


Vertical  face  of  loess  in  railway  cutting  near  Bertram,  Iowa. 


DISTRIBUTION   OP  BOWLDERS  OF  IOWAN  AREA  125 

Topographic  Distribution — Some  writers  have  described  these 
bowlders  as  being  confined  principally  to  swales,  or  depressions 
in  the  slopes,  and  from  this  it  has  been  inferred  by  some  that 
most  of  the  bowlders  are  the  residue  left  on  the  removal  of  con- 
siderable drift  by  erosion  when  the  broad  open  swales  were  be- 
ing formed.  It  is  true  that  most  of  the  bowlders  left  scattered 
on  the  land  at  the  present  time  lie  in  these  swales,  yet  the 
writers'  observations  show  that  many  erratics,  both  large  and 
small,  do  occur  on  the  uplands  as  well  as  in  swales.  This  leads 
them  to  the  opinion  that  originally  the  bowlders  were  scattered 
indiscriminately  over  uplands,  slopes  and  swales.  Since  the  re- 
gion has  been  occupied  by  white  men,  however,  nearly  all  the 
bowlders  have  been  gathered  from  the  tracts  desired  for  cultiva- 
tion, both  in  order  to  clear  the  land  and  in  order  to  use  the  stone 
for  foundations  of  buildings  and  abutments  for  bridges.  Over 
a  large  part  of  the  area  the  ground  water  level  is  so  high  that 
except  in  the  driest  seasons  water  seeps  out  of  the  lower  slopes 
and  in  the  bottoms  of  the  shallow  swales.  These  tracts,  being 
wet  lands,  are  not  generally  cultivated  but  are  reserved  as 
pastures  for  stock,  and  the  farmers  have  not  taken  the  trouble 
to  remove  the  bowlders  therefrom ;  hence  at  present  most  of  the 
scattered  bowlders  lie  in  the  swales.  The  typical  lowan  topog- 
raphy is  apparently  not  due  primarily  to  erosion  since  the  last 
ice  disappeared  from  the  area,  but  is  the  result  of  mantling  of 
an  older  mature  erosion  topography  with  a  post-Kansan  sheet 
of  drift.  It  thus  appears  that  the  bowlders  in  the  swales  can  not 
be  regarded  as  the  residuum  of  a  much  eroded  drift  sheet,  and 
their  presence  in  the  swales  can  not  be  regarded  as  evidence  of 
much  erosion.  Most  of  the  bowlders  evidently  were  left  by  the 
melting  ice  on  the  surface  of  the  drift  where  they  lay  before  man 
began  his  collection  of  them.  Some  are  wholly  or  partly  buried 
in  the  drift. 

Doctor  Calvin  and  others  have  shown  that  some  of  these 
bowlders  have  beveled  surfaces  and  bear  glacial  striations,  and 
thus  show  that  they  were  transported,  for  a  time  at  least,  in 
the  basal  part  of  the  ice.  Such  striations  were  observed  by  the 
writers  also.  It  is  probable  that  the  striations  on  many  bowlders 
have  been  obscured  by  etching  and  exfoliation,  inasmuch  as  the 


126  THE   IOWAN   DRIFT 

striae  seen  are  in  most  cases  on  surfaces  which  have  been  but 
recently  uncovered  by  excavation. 

Character  of  the  Embedding  Till. — Borings  were  made  by  the 
side  of  several  partly  buried  big  bowlders  to  determine  the 
character  of  the  embedding  drift.  These  showed  that  the  drift 
is  the  same  yellow,  moderately  weathered  till,  which  is  leached 
to  depths  of  three  to  five  feet,  as  seen  in  most  of  the  exposures, 
and  which  is  regarded  as  lowan. 

Bowlders  in  the  Kansan  Area 

There  seems  to  have  been  a  general  impression  that  the  large 
granite  bowlders  in  Iowa  are  strictly  confined  to  the  lowan  drift 
area.15  Indeed,  the  presence  of  large  granite  bowlders  in  some 
outlying  tracts  has  been  taken  to  indicate  the  presence  of  lowan 
drift.  The  supposed  lobe  of  lowan  drift  in  southwestern  Tama 
county  was  mapped  partly  because  of  the  presence  of  such 
bowlders16.  And  in  Jasper  county,  in  certain  townships  which 
have  the  aspects  of  Kansan  topography,  the  occurrence  of  one 
bowlder  with  a  diameter  of  thirty  feet  and  of  other  large  ones 
of  granitic  composition  led  Mr.  I.  A.  Williams  to  postulate  an 
extension  of  the  lowan  ice  into  that  area  to  explain  their 
presence17. 

It  appears,  however,  that  occasional  large  granite  bowlders 
occur  farther  south  in  Iowa,  some  of  them  remote  from  the 
lowan  drift  area  (figure  11).  Several  erratics  with  diameters 
of  ten  to  thirty  feet  have  been  reported  from  Lucas  county.18  In 
section  32  of  Center  township,  Wapello  county,  A.  Gr.  Leonard 
found  a  fine-grained  granite  measuring  six  by  twelve  by  five 
feet19.  J.  A.  Udden  reports  finding  in  section  15  of  Walnut 
township,  Jefferson  county,20  a  porphyritic  granite  seventeen 
by  twelve  by  seven  feet  in  size.  Besides  these  some  granites 
ten  feet  in  diameter  were  noted  in  Henry  county.21 

During  the  present  investigation  several  other  large  bowlders 
were  seen  in  the  Kansan  area.  Of  these,  three  were  in  Marshall 

"Calvin,  Samuel,  The  lowan  drift:  Jour.  Geology,  Vol.  XIX,  p.   599,  1911. 

"Savage,  T.  E.,  Iowa  Geological   Survey,  Vol.  XIII,   p.   200,   1903. 

"Iowa   Geological   Survey,   Vol.   XV,   pp.    288-290,    1905. 

!(iKay,  G.  F.,  in  a  personal  communication. 

"Iowa  Geological  Survey,  Vol.  XII.  p.  439.  1902. 

'"Iowa   Geological   Survey.   Vol.    XII,   p.    358,    1902. 

"Savage,  T.  E.,  Iowa  Geological  Survey,  Vol.  XII,  p.  420,   1902. 


BOWLDERS  AS  EVIDENCE  OF  IOWAN  GLACIATION  127 

county ;  one  in  Logan  township  in  the  southeast  quarter  of  sec- 
tion 4,  which  measured  ten  by  four  by  six  feet ;  one  in  the  central 
part  of  section  8,  Eden  township,  which  measured  fifteen  by 
fifteen  by  three  feet ;  and  one  in  the  southwest  quarter  of  section 
33,  Timber  creek  township,  which  measured  eight  by  five  by 
three  feet.  In  Jasper  county  a  bowlder  with  a  diameter  of  ten 
feet  was  seen  protruding  from  a  cut  on  the  Chicago,  Rock  Island 
and  Pacific  railway,  six  miles  east  of  Kellogg.  In  Cedar  county, 
in  the  northwest  quarter  of  section  21,  Gower  township,  another 
bowlder  with  a  diameter  of  ten  feet  was  found.  McGee  re- 
ported22 other  large  bowlders  as  occurring  near  Davenport, 
Iowa.  Big  bowlders  also  occur  in  the  northwest  and  southwest 
parts  of  Jackson  county,  near  Epworth  in  Dubuque  county,  and 
in  Clinton  county,  at  places  to  which  it  is  doubtful  if  the  lowan 
ice  extended. 

Professor  Savage23  also  reports  considerable  numbers  of 
bowlders  as  occurring  northeast  of  Maquoketa  in  Jackson 
county.  "Many  of  these, ' '  he  states,  ' ' are  of  exceptionally  large 
size  for  drift  of  their  age  (Kansan),  the  larger  masses  having 
a  diameter  of  six  to  nine  feet." 

Big  Bowlders  As  Evidence  of  lowau  Glaciation 

Inasmuch  as  large  granite  bowlders  occur  outside  the  lowan 
drift  area,  it  is  apparent  that  some  such  bowlders  were  carried  by 
the  Kansan  drift  There  is,  therefore,  some  question  as  to  how 
far  the  big  bowlders  within  the  supposed  limits  of  the  lowan  drift 
can  be  regarded  as  evidence  of  a  distinct  post-Kansan  ice  in- 
vasion. 

In  this  connection  it  is  well  to  consider  the  direction  of  move- 
ment of  the  Kansan  ice  which  spread  over  the  eastern  half  of 
the  state  (figure  11).  Several  observations  of  glacial  striae  have 
been  noted.  In  1914  striae  were  found  on  limestone  underlying 
the  Kansan  drift  at  Kuhnle's  quarry  at  Charles  City,  Floyd 
county,  trending  south-southeast.  Professor  S.  W.  Beyer24  ob- 
served strife  in  Marshall  county,  in  LeGrand  and  Timber  Creek 
townships,  trending  south  20°  to  25°  east.  Professor  W.  H. 

STL   S.  Geol.   Survey  Eleventh  Ann.  Kept,  o.   482 

"Savage.   T.   B..  Iowa  Geological   Survey,  Vol.  XVI    p.    634,    1906. 

=»Iowa  Geological   Survey,  Vol.  VII,  PP.   239-240,  1897. 


128  THE   IOWAN   DRIFT 

Norton25  found  two  sets  of  striae  at  the  quarry  one  and  one- 
fourth  miles  northeast  of  Quarry  Station  (Section  1,  LeGrand 
township,  Township  83  North,  Range  17  West) ;  one  bearing 
south  22°  east  to  south  47°  east;  the  other,  south 
35°  to  64°  west.  Dr.  H.  F.  Bain20  reports  the  observation  of  striae 
at  Eddyville  near  the  south  line  of  Mahaska  county.  These  con- 
sisted of  an  earlier  set  trending  south  42°  east  and  a  later  set 
trending  south  70°  east.  Doctor  J.  A.  Udden27  observed  obscure 
striag  northeast  of  Perlee  in  northeastern  Jefferson  county. 
The  trends  are  given  as  south  35°  east,  and  south  75°  west. 
Possibly  the  direction  of  movement  making  the  latter  may 
have  been  north  75°  east,  since  so  westerly  a  direction  of  move- 
ment at  this  place  of  either  the  Kansan  or  pre-Kansan  ice  seems 
rather  doubtful,  while  local  northeasterly  deflection-  is  quite 
possible. 

At  Brighton  in  southwestern  Washington  county  stria?  report- 
ed by  H.  F.  Bain28  trend  south  4"  to  6°  east  with  a  few  scratches 
south  6°  west  to  south  4°  east.  Not  far  away  on  Crooked  creek 
striae  were  seen  trending  south  67°  east.  In  a  paper  " Glacial 
scorings  in  Iowa,"  G.  R.  Keyes29  cites  observations  of  striae  near 
'  Iowa  Gity,  as  reported  by  McGee,  Calvin,  and  others,  trending 
south  52°  to  62°  east.  Striae  trending  south  70°  to  73°  east  were 
observed  also  near  the  western  end  of  the  electric  railway  bridge 
at  Iowa  City  by  W.  C.  Alden. 

W.  H.  Norton30  discovered  striae  at  an  old  cut  on  the  Chicago, 
Milwaukee  &  St.  Paul  railway  five  miles  northwest  of  Cedar 
Rapids,  Linn  county,  (one  mile  west  of  Linn  Junction)  ranging 
south  79°  east  to  east  14°  north. 

In  1915  W.  C.  Alden  observed  a  finely  glaciated  ledge  recently 
exposed  in  grading  a  road  six  miles  east  of  Delmar,  Clinton 
county  (Waterford  township,  Township  83  North,  Range  4  East, 
section  21,  southeast  quarter).  Here  the  striae  trend  east  10° 
north. 

^lowa  Scad.  Science,  Vol.  18,  pp.  80-83,  1911. 
*Iowa  Geological   Survey,  Vol.  IV.  p.  343.   1895. 
27Iowa  Geological  Survey,  Vol.   XII,  p.    431,    1902. 
""Iowa  Geological   Survey,  Vol.  V,  p.   155,   1896. 
^Towa  Geological   Survey.   Vol.   III.  pp.   148-165,    1894. 
3nlowa,  Acad.  Science,  Vol.   18,  pp.  80-83,  1911. 


DIRECTION  OF  ICE  MOVEMENT  IN  EASTERN  IOWA  129 

Somewhat  doubtful  striae  bearing  east  43°  north  were  seen  by 
the  writers  on  a  limestone  ledge  in  the  road  at  a  point  about  one 
mile  southwest  of  Monticello,  Jones  county  (Monticello  town- 
ship, Township  86  North,  Range  3  West,  section  33,  northeast 
quarter). 

If  these  several  striae,  or  even  most  of  them,  were  made  by 
the  Kansan  ice,  as  seems  probable  since  most  of  them  are  out- 
side the  area  of  the  lowan  drift,  they  show  something  as  to  the 
direction  of  the  ice  flow  reaching  these  parts  of  Iowa.  If  one 
may  judge  from  these  as  well  as  from  general  consideration  of 
the  eastern  limit  of  the  drift  in  northeastern  Iowa,  the  Kansan 
ice  in  the  eastern  half  of  the  lobe  which  invaded  Iowa  radiated 
eastward,  the  directions  of  flow  shifting  from  south  20°  or  25° 
east  in  Marshall  county,to  south  70°  to  73°  east  in  Johnson 
county,  east  10°  north  in  northern  Clinton  county,  and  thence 
in  northeastern  Iowa  also  toward  the  east.  Ice  currents  cross- 
ing Johnson  county  thus  must  have  swung  eastward  to  the 
vicinity  of  Muscatine  and  Davenport.  Thus  the  main  stream  of 
Kansan  ice  which  crossed  northeastern  Iowa  where  are  now 
most  of  the  big  bowlders,  probably  did  not  reach  the  Kansan 
area  south  of  the  lowan  drift  boundary.  Some  big  bowlders 
certainly  were  carried  by  the  Kansan  ice.  If  only  that  part  of 
the  ice  flow  which  spread  over  northeastern  Iowa  crossed  the 
ledges  yielding  most  of  the  massive  blocks  of  granite,  the  dis- 
tribution of  the  big  bowlders  would  be  such  as  we  now  find  it 
to  be  even  had  there  been  no  post-Kansan  ice  invasion.  The  big 
bowlders  of  southern  Iowa  are  few  but  it  was  also  noted  that 
the  big  bowlders  are  much  less  abundant  in  the  southern  part  of 
the  lowan  drift  area  west  of  Linn  county  than  farther  north, 
so  that  if  such  bowlders  were  carried  by  the  Kansan  ice  it 
might  be  expected  that  but  few  would  be  seen  in  the  Kansan  area 
west,  southwest,  and  south  of  Johnson  county. 

Judging  from  their  distribution  alone,  therefore,  it  would 
seem  that  the  big  lowan  bowlders  could  just  about  as  well  be  re- 
ferred to  transportation  and  deposition  by  the  Kansan  ice  as 
by  the  post-Kansan  glacier.  The  writers  are  therefore  not  in- 
clined to  place  very  much  weight  on  these  erratics,  taken  by 
themselves,  as  evidence  of  a  distinct  post-Kansan  glaciation  of 


130  THE   IOWAN   DRIFT 

northeastern  Iowa.  It  is,  however,  a  notable  fact  that  by  far 
the  larger  part  of  the  big  bowlders  of  Iowa,  probably  99  per  cent 
of  them,  occur  within  the  supposed  limits  of  the  lowan  drift, 
and  taken  in  connection  with  the  other  evidence  they  may  be 
said  to  support  the  theory  of  a  post-Kansan  glaciation. 


CHAPTER  VI. 
IOWAN  OUTWASH  AND  OTHER  GRAVELS, 

In  accordance  with  the  evidence  already  presented  which  in- 
dicates that  there  really  is  an  lowan  drift-sheet,  it  would  be 
expected  that  out-wash  gravels  of  post-Kansan  and  pre-Wiscon- 
sin  age  would  be  found  in  valleys  which  received  the  drainage 
from  the  lowan  ice. 

VALLEY  TRAIN  TERRACES. 

In  practically  all  of  the  valleys  of  northeastern  Iowa  there 
are  gravel  deposits.  A  few  of  the  valleys  head  in  the  area  of  the 
Wisconsin  drift  and  much  of  the  gravel  in  these  probably  is 
Wisconsin  outwash.  The  rest  of  the  valleys,  however,  head  in 
the  lowan  drift  area  and  much  of  the  gravel  in  these  probably 
is  lowan  outwash. 

It  may  be  well  to  give  some  details  as  to  the  occurrences  of 
gravels  near  and  outside  of  the  limit  of  the  lowan  drift.  These 
deposits  were  carefully  examined  at  many  places.  None  of  the 
valleys  was  studied  throughout  its  full  extent  and  the  relations 
to  the  gravel  deposits  on  Mississippi  river  have  not  been  de- 
termined. 

Starting  at  the  north  in  Howard  county,  a  gravel  terrace  was 
observed  fifteen  to  twenty  feet  above  Upper  Iowa  river  at  and 
west  of  Florenceville,  Iowa,  and  Grainger,  Minnesota.  Near  the 
state  line  a  cut  south  of  the  bridge  showed  coarse  gravelly 
material  composed  mostly  of  limestone  fragments,  partly  angu- 
lar and  partly  waterworn,  with  some  intermingled  crystalline 
pebbles,  but  the  gravels  here  appeared  more  like  the  material  of 
a  local  alluvial  fan  than  glacial  outwash.  Ten  Mile  creek  heads 
in  a  broad  open  swale  east  of  Ridgeway.  At  the  point  where  the 


GRAVEL  TERRACES  ALONG  UPPER  IOWA  RIVER 


131 


lowan  drift  boundary  has  been  mapped  as  crossing,  the  valley 
narrows  sharply  and  the  stream  enters  a  gorge  between  bluffs 
of  shale.  One  would  expect  to  find  here  a  well-marked  deposit 
of  gravel  washed  out  from  the  lowan  ice  front,  but  none  was 
noted  in  the  two  or  three  miles  traversed. 

There  is  some  development  of  a  terrace  in  the  Upper  Iowa 
river  valley  above  Decorah,  but  this  was  not  examined.  Well 
marked  terraces  occur  at  points  below  this  place.  About  a  mile 
north  of  Freeport  interesting  exposures  of  old  drift  and  of 
fresher  gravel  were  seen.  The  relations  are  shown  in  figure  12. 


Fig.  12. — Diagram  showing  terraces  on  Upper  Iowa  river  near  Freeport,  Iowa.  Loess 
(1);  old  weathered  drift  (Kansan?)  (2);  outwash  gravel  from  lowan 
drift  (3)  ;  limestone  (4).  i 

At  this  place  (Decorah  township,  Township  98  North,  Range  8 
"West,  section  12,  southwest  quarter)  A.  M.  Sheets  has  a 
gravel  pit  in  a  remnant  of  a  terrace  just  below  the  road.  The 
stratified  sand  and  gravel  exposed  here  (eight  feet)  are  fresh, 
clean,  and  unoxidized.  The  pebbles  are  largely  of  limestone 
with  intermingled  cherts,  quartzites  and  crystallines.  It  seems 
probable  that  this  fresh-looking  gravel  is  outwash  to  be  cor- 
related with  the  lowan  stage  of  glaciation.  The  house  stands  on 
a  terrace  just  south  of  the  road  at  about  the  same  level,  but 
underlain  by  limestone  and  sandstone.  Just  west  of  the  house 
and  above  the  terrace,  deeply  weathered  red  gravelly  drift  is 
exposed  in  the  road  cut.  No  limestone  pebbles  were  found  in 
this,  only  cherts,  quartzites  and  dense  fine-grained  crystallines. 
It  is  probable  that  this  is  at  least  as  old  as  the  Kansan  stage, 
as  is  also  that  on  top  of  the  bluff  near  the  Freeport  bridge. 
Farther  down  the  valley  in  Glenwood  township,  (Township  98 


132  THE   IOWAN   DRIFT 

North,  Range  7  West)  limestone  gravels  were  seen  at  several 
points,  notably  at  the  new  dam  and  powerhouse  in  section  8. 

Doctor  Calvin31  describes  these  gravels,  referring  to  them  as 
"  deposits  of  uncertain  age,  probably  Kansan."  He  writes, 
"  Along  the  river  from  the  county  line  westward,  in  the  south- 
east quarter  of  section  36,  Pleasant  township,  the  terraces  are 
well  developed.  Not  far  from  the  line  the  stratified  terrace 
materials  have  been  undercut  by  the  river  so  as  to  show  a  fresh 
section  forty  feet  in  height.  Near  and  below  the  middle  of  the 
section  there  are  many  coarse  blocks  from  the  Oneota  and  Saint 
Peter  formations,  but  the  main  body  of  the  deposit  consists  of 
rounded  fragments  of  chert  and  local  limestone,  with  some 
pebbles  of  quartz,  diorite,  granite  and  other  northern  crys- 
tallines, all  embedded  in  quartz  sand.  Some  small  streaks  made 
up  almost  exclusively  of  northern  pebbles  and  quartz  sand  are 
iron  stained  and  resemble  the  ordinary  Buchanan  gravels.  Be- 
tween section  36  of  Pleasant  township  and  section  16  of  Decorah, 
there  are  many  remnants  of  the  same  terrace  deposits." 
Doctor  Calvin  regarded  only  the  deposits  of  fresh  clean  sand, 
such  as  that  on  the  southeast  side  of  the  valley  northeast  of 
Freeport,  as  outwash  from  the  lowan  ice. 

There,  is  a  gravel  terrace  on  North  Branch  of  Turkey  river 
south  of  Cresco  (section  2,  New  Oregon  township),  fifteen  feet 
above  the  stream.  Similar  deposits  were  also  seen  at  points 
farther  down  stream  in  Winneshiek  county,  west  and  southwest 
of  Eidgeway.  Four  miles  south  of  this  place  (Sumner  town- 
ship, Township  97  North,  Range  10  West,  section  11,  northeast 
quarter)  the  sand  and  gravel  terrace  stands  twenty  feet  above 
the  stream.  At  and  near  Spillville  is  a  fifteen-foot  gravel 
terrace.  Below  this  the  valley  is  largely  a  narrow  winding 
gorge.  Remnants  of  the  terrace  were  seen  down  to  and  below 
Fort  Atkinson.  This  place  stands  on  a  bench  which  appears 
to  be  underlain  by  gravel.  About  two  miles  farther  southeast 
and  one  and  one-half  miles  west  of  Festina,  the  gravel  terrace 
is  well  developed  near  the  bridge.  Twenty  feet  above  the 
present  flood  plain  an  exposure  in  the  cut  bank  showed  two  feet 
of  brown  loamy  soil  overlying  the  gravel  from  which  the  lime- 

«Iowa  Geological  Survey,  Vol.  XVI,  p.  124. 


GRAVEL  TERRACES  ALONG  TURKEY  RIVER  VALLEY  133 

stone  pebbles  had  been  removed  by  solution  to  a  depth  of  six 
feet  (that  is,  eight  feet  from  the  surface).  Below  this  the  gravel 
contains  plenty  of  waterworn  pebbles  of  limestone  and  some 
angular  fragments.  Gravels  head  in  some  of  the  tributaries  on 
the  west,  but  one  is  somewhat  surprised  not  to  see  them  more 
markedly  developed  in  situations  where  there  were  such  direct 
lines  of  drainage  from  the  lowan  ice  front. 

The  streams  at  and  near  Waucoma  are  bordered  by  a  gravel 
terrace  about  twelve  feet  above  the  flood  plain.  At  one  point 
where  an  examination  was  made  no  limestone  pebbles  were 
noted  within  eight  feet  of  the  surface.  In  Fayette  county  a 
terrace  is  well  preserved  above,  at  and  below  Eldorado,  in  which 
the  gravel  is  largely  composed  of  limestone  pebbles.  Near  the 
bridge  in  section  35,  Dover  Township  (Township  95  North, 
Eange  8  West),  this  bench  stands  about  thirty  feet  above  the 
stream  and  there  are  plenty  of  limestone  pebbles  with  the  crys- 
tallines. There  is  also  a  large  terrace  remnant  at  the  east  line  of 
the  township.  The  towns  of  C'lermont  and  Elgin  stand  on  broad 
remnants  of  this  terrace.  The  Chicago,  Rock  Island  &  Pacific 
Railway  has  a  large  pit  in  the  well  stratified  gravels  north  of 
Elgin.  At  the  latter  place  the  terrace  is  about  twenty  feet  above 
the  broad  flood  plain.  Where  they  were  examined  near  the 
cemetery,  the  gravels  are  rusty  in  the  upper  part,  but  the  crys- 
talline pebbles  are  fresh  and  sound  and  limestone  pebbles  were 
plentiful  below  five  feet  from  the  surface. 

In  his  report  on  Fayette  county32  Prof.  T.  E.  Savage  referred 
the  deposition  of  these  gravels  to  waters  from  the  Kansan  ice 
sheet.  Those  seen  by  the  writers,  however,  appear  quite  fresh 
enough  to  be  correlated  with  the  lowan  stage  of  glaciation. 
In  his  recent  volume  on  the  Pleistocene  Mammals  of  Iowa33 
Dr.  0.  P.  Hay  makes  the  following  reference  to  these  gravels : 

Near  Clermont.  In  Nettie  C.  Anderson's  list,  page  28,  Prof. 
T.  E.  Savage  reported  a  mastodon  tooth  from  near  Clermont, 
which  was  in  the  possession  of  Mr.  C.  E.  Allen,  of  Clermont. 
Mr.  Allen  has  sent  the  writer  a  drawing  which  shows  that 
the  tooth  is  that  of  Elephas,  probably  Elephas  primigenius. 
Professor  Savage  has  kindly  informed  the  writer  that  the  tooth 

32Iowa  Geological  Survey,  Vol.  XV,  pp.  451-53. 

"Iowa  Geological   Survey,   Vol.   XXIII,  pp.    433   and  434,    1913. 


134  THE  IOWAN  DRIFT 

came  from  materials  filling  the  valley  of  Turkey  river.  He 
believes  that  these  were  deposited  during  the  melting  of  the 
Wisconsin  ice-sheet.  If  this  is  true,  the  animal  which  bore  the 
tooth  lived  at  the  close  of  the  Wisconsin  stage  or  afterwards. 
Near  this  same  place  was  found  a  part  of  a  skull  of  the  musk-ox 
Ovibos  moschatus.  Mr.  Allen  states  that  the  tooth  was  taken 
out  of  the  gravel  pit  of  the  Bock  Island  Eailway  between  Cler- 
mont  and  Elgin,  Iowa,  and  that  it  was  found  at  a  depth  of  about 
twenty  feet.  The  tooth,  or  what  remains  of  it,  is  in  the  posses- 
sion of  Mr.  Allen. 

The  present  writers  regard  this  gravel  as  of  lowan  rather 
than  Wisconsin  age.  The  terrace  is  reported  by  Prof.  A.  Gr. 
Leonard34  to  be  fifty-five  feet  above  the  stream  at  Elkader, 
where  much  of  the  town  east  of  the  river  is  built  upon  it,  and 
at  Osterdock  it  is  sixty  feet  above  the  river. 

The  valley  of  Otter  creek  between  West  Union  and  Elgin  was 
pot  examined  for  outwash  gravels. 

Volga  river,  a  tributary  of  Turkey  river,  receives  drainage 
from  the  lowan  area  from  the  vicinity  of  West  Union  to 
Edgewood  in  southwestern  Clayton  county.  The  lower  part  of 
Fayette  is  built  on  a  well  marked  terrace  ten  to  fifteen  feet 
above  this  stream  and  below  the  bench  on  which  stands  Upper 
Iowa  University.  At  the  mouth  of  this  branch  of  the  valley  at 
Albany  is  a  broad  gravel  terrace. 

At  and  above  Wadena  the  gravel  terrace  is  twenty-five  to 
thirty  feet  above  the  stream.  The  main  part  of  Volga  stands 
on  a  terrace  of  fine  gravel  which  occupies  a  broad  abandoned 
channel  surrounding  the  low  hill  on  which  is  the  cemetery. 
West  of  town  a  pit  in  the  edge  of  the  terrace  showed  three  feet 
of  sand  over  five  feet  of  sand  and  fine  iron  stained  calcareous 
gravel.  This  terrace  is  twenty  or  thirty  feet  above  the  present 
stream. 

The  tributaries  from  the  south  have  a  fall  of  300  to  400  feet 
in  distances  of  three  to  six  miles  between  the  border  of  the 
lowan  drift  and  Volga  river.  They  are  in  sharply  cut  valleys 
which,  so  far  as  was  seen,  do  not  contain  outwash  deposits. 
They  were  not,  however,  carefully  examined.  From  a  point 
about  three  miles  east  of  Greeley,  Delaware  county,  southeast 

"Iowa  Geological  Survey,  Vol.  XVI,  pp.  287-288. 


GRAVEL  TERRACES  ALONG  MAQUOKETA  RIVER  135 

nearly  to  Dyersville  the  drainage  is  toward  rather  than  away 
from  what  has  been  mapped  as  the  lowan  border. 

A  gravel  terrace  stands  twelve  to  twenty  feet  above  the 
streams  just  north  and  northwest  of  Dyersville,  also,  south  of. 
this  place  and  at  Worthington.  With  these  may  belong  the 
terrace  gravels  seen  on  the  same  stream  at  Fulton  and  Hurst- 
ville,  north  of  Maquoketa  in  Jackson  county.  • 

Well  preserved  remnants  of  terrace  gravels  were  examined 
at  many  places  along  Maquoketa  river  from  Manchester  to 
Maquoketa.  The  former  place  is  built  upon  a  broad  flat  beneath 
which  wells  penetrate  as  much  as  forty  feet  of  gravel,  an  amount 
sufficient  to  divert  the  river  over  limestone  ledges.  Southeast  to 
Hopkinton  the  terrace  stands  twenty  to  twenty-five  feet  above  the 
stream.  The  gravels  are  well  exposed  at  the  mouth  of  the  gorge 
traversed  by  Lime  creek  and  also  west  of  the  point  where  this 
stream  enters  the  gorge  on  its  way  down  from  the  upland. 
Doctor  Calvin35  in  describing  the  terrace  states  that  ''excava- 
tions show  that  the  main  body  of  this  terrace  is  made  up  of 
very  old,  weathered,  ferruginous  material  of  the  age  of  the 
Buchanan  gravels";  also: 

It  is  interesting  to  note  that  the  terraces  observed  in  this 
county  are  nearly  all  referable  to  the  period  of  ice  melting 
following  the  invasion  of  the  Kansan  glaciers.  In  some  cases 
there  have  been  some  additions  to  the  terrace  deposits  in  times 
more  recent  than  the  Buchanan  gravels,  but  the  significant  point 
is  that  these  valleys  are  pre-Kansan  in  origin. 

The  gravels  where  seen  by  the  present  writers  seem  not  too 
old  to  be  regarded  as  lowan,  while  other  evidence  cited  above 
(page  71)  seems  to  show  that  the  valley  cut  in  the  limestone  is 
itself  of  post-Kansan  rather  than  pre-Kansan  age,  at  least  in 
the  part  examined. 

Four  miles  south  of  Lime  creek,  only  the  upper  leached  part 
of  the  gravel  was  seen. 

At  -and  north  of  Monticello  the  terrace  is  well  preserved. 
Exposures  show  the -.gravels  to  be  well  stratified  and  cross- 
bedded.  They  are  noncalcareous,  partly  fresh  and  partly  rusty. 
Though  the  gorge  below  Monticello  is  narrow  and  winding 
remnants  of  the  terrace  were  noted  at  many  points.  The  pebbles 

35Iowa  Geological  Survey,  Vol.  VIII,  p.  176. 


136  THE  IOWAN  DRIFT 

in  the  sand  are  mostly  fine  but  range  in  size  up  to  eight  or  ten 
inches ;  the  crystalline  pebbles  are  mostly  sound  and  hard,  not 
much  decomposed.  But  few  limestone  pebbles  were  found. 
The  village  of  Canton  at  the  east  line  of  Jones  county  stands 
on  a  bit  of  this  terrace. 

A  terrace  near  Newport  is  well  preserved  and  north  of  Olin 
on  Wapeipinicon  river,  and  at  the  bridge  between  Hale  and 
Oxford  is  a  terrace  of  fine  sand  and  gravel  twelve  to  thirteen 
feet  above  the  stream. 

Rochester,  on  Cedar  river  south  of  Tipton,  stands  on  a  gravel 
terrace,  but  not  much  attention  was  given  to  deposits  along  this 
stream.  Some  of  these,  such  as  those  on  the  broad  flat  opposite 
and  above  Cedar  Bluff,  may  have  resulted  from  slackwater 
during  the  Illinoian  stage.  Such  slackwater  must  have  occupied 
the  valley  as  far  up  as  Ivanhoe  bridge  southwest  of  Mount 
Vernon. 

In  the  Iowa  river  valley,  below  the  North  Liberty  lobe,  there 
are  terrace  remnants  of  probable  lowan  age.  It  does  not  seem 
likely  that  these  are  Wisconsin,  since  terraces  of  that  age  play 
out  before  reaching  Marshalltown  and  since  the  terraces  to 
which  reference  is  here  made  are  mere  remnants  at  the  bends 
of  the  stream.  A  similar  terrace  on  Pardieu  creek  about  four 
miles  north  of  Iowa  City  (Penn  township,  Township  80  North, 
Range  6  West,  section  29)  is  regarded  by  Mr.  Leighton  as  com- 
posed of  outwash  from  the  North  Liberty  lobe  of  the  lowan  ice.38 

The  gravels  distributed  along  the  courses  of  the  streams 
within  the  lowan  area,  but  which  do  not  head  in  the  Wisconsin 
drift  area,  were  probably  deposited  by  the  outflowing  waters 
as  the  margin  of  the  lowan  ice  sheet  retreated  across  the  area 
during  the  final  stage  of  melting.  Such  gravels  are  well  de- 
veloped in  the  Wapsipinicon  river  valley  at  Central  City,  Linn 
county,  at  Quasqueton,  Buchanan  county,  and  east  of  New 
Hampton,  Chickasaw  county;  in  the  Little  Cedar  river  valley 
at  Bassett,  Chickasaw  county,  at  Stacyville,  Mitchell  county, 
and  in  the  valleys  of  numerous  small  streams. 

State  of  weathering. — As  noted  above,  these  gravels  are  un- 
consolidated  and  moderately  fresh  in  appearance.  Decayed 

^Leighton,  M.  M.(  Additional  evidences  of  Post-Kansan  glaciation  in  Johnson 
County,  Iowa:  Pi-oc.  Iowa  Acad.  Sci.,  Vol.  20,  pp.  251-256,  1913. 


UPLAND  GRAVELS  IN  THE  IOWAN  AREA  137 

pebbles  and  whole  ironstone  concretions  are  comparatively  few, 
though  there  are  numerous  fragments  of  ironstone  concretions, 
as  if  these  had  been  derived  from  such  older  gravel-bodies  as 
the  Buchanan.  The  amount  of  solution  which  the  limestone 
pebbles  have  suffered  is  considerable.  This  varies  according 
to  the  coarseness  of  the  material.  Fine  sandy  gravel  commonly 
contains  no  limestone  pebbles  in  the  upper  ten  to  twelve  feet, 
whereas  in  coarser  materials  calcareous  constituents  have  been 
removed  to  depths  of  three  to  five  feet.  Gravel  of  the  latter  sort 
was  exposed  in  the  Chicago,  Anamosa  &  Northern  Railway  pit 
near  the  depot  in  Quasqueton,  Buchanan  county,  on  a  terrace 
of  Wapsipinicon  river.  The  upper  three  to  four  feet  of  the 
gravel  contain  cherts,  greenstones,  granites,  dense  igneous  rocks, 
and  quartz,  with  no  limestone,  whereas  below  there  are  many 
irregular  fragments  of  limestone  as  large  as  four  to  six  inches. 

In  Chickasaw  county,  one  mile  west  of  Bassett,  the  Chicago, 
Milwaukee  &  St.  Paul  Railway  has  a  large  gravel  pit  nearly 
fifteen  feet  deep  in  a  well  developed  terrace  bordering  Little 
Cedar  river.  The  gravel  consists  mostly  of  pebbles  half  an  inch 
to  an  inch  and  a  half  in  diameter.  The  limestone  constit- 
uents seem  to  have  been  removed  by  solution  to  depths  of  eight 
to  twelve  feet  from  the  surface. 

TH/E  ABSENCE  OF  GLAOIO-FLUVIAL  GRAVEL  IN  CERTAIN  VALLEYS  OF 
THE  KANSAN  AREA. 

It  appears  from  the  literature  of  the  Kansan  drift  of  southern 
Iowa  that  there  is  a  general  absence  of  gravel  terraces  from 
that  area.  So  far  as  the  present  writers  have  had  opportu- 
nity to  examine  the  valleys  this  seems  to  be  true  of  those  which 
do  not  reach  into  areas  of  younger  drift.  This  opposes  an 
interpretation  which  regards  the  gravels  described  above  as  due 
to  increased  erosion  of  drift  on  the  slopes  and  deposition  in  the 
valleys  during  the  Wisconsin  stage  or  at  any  other  post-Kansan 
time.  The  lack  of  erosional  details  on  the  slopes  of  the  lowan 
drift  also  opposes  this  view.  These  gravel  terraces  are,  there- 
fore, regarded  by  the  present  writers  as  composed  of  glacial 
outwash  of  lowan  age. 

UPLAND  GRAVEL. 

Two  phases  of  upland  gravel  were  found  throughout  the 
lowan  area,  which  appear  to  be  of  two  distinct  ages :  Kansan 
and  lowan. 


138  THE   IOWAN   DRIFT 

lowan  Kames. — Reference  is  elsewhere  made  to  the  oc- 
currence of  morainal  knolls  of  relatively  fresh  .gravel  in 
Winneshiek  county.  Besides  these,  knolls  of  similar  material 
were  seen  in  Howard  county,  Sumner  township,  in  the  east- 
central  part  of  section  5  and  the  west-central  part  of  section  4 ; 
and  in  Mitchell  county,  Cedar  township,  in  the  northwest  quarter 
and  northeast  quarter  of  section  5.  Deposits  of  upland  gravel, 
not  in  distinct  knolls  and  showing  moderate  weathering,  were 
also  examined  in  Linn  county,  Jackson  township,  central  part 
of  section  21,  and  in  Delaware  county,  Oneida  township,  west 
line  of  the  southwest  quarter  of  the  northwest  quarter  of  section 
12.  Limestone  pebbles  are  present  in  most  of  these  below  depths 
of  three  to  five  feet.  Comparison  of  the  amount  of  weathering 
of  the  upland  gravels  and  of  the  gravel  terraces  of  the  lowan 
area,  taking  into  consideration  their  topographic  positions,  in- 
dicates that  the  gravels  are  probably  of  the  same  age. 

Kansan  Kames. — At  many  places  in  the  lowan  area,  and 
especially  in  Buchanan  county  near  Independence,  there  are  low 
rounded  knolls  on  the  upland  which  apparently  belong  to  an 
older  deposit.  These  knolls  contain  highly  oxidized  and  decayed 
ferruginous  gravels,  with  an  abundance  of  ironstone  concretions 
and  disintegrated  granites,  greenstones,  and  other  igneous  rocks. 
The  surfaces  of  some  of  the  quartzites  even  show  etching.  Cal- 
careous material  is  generally  lacking,  having  been  removed  by 
solution.  Everywhere  the  gravels  have  a  distinct  brown  color, 
and  in  all  respects  show  great  age.  The  materials  range  in 
size  from  sand  to  small  bowlders  a  foot  in  diameter.  The  smaller 
pebbles,  and  many  of  the  larger  ones,  can  readily  be  cut  in  two 
by  a  chisel-edged  hammer.  These  gravels  are  better  for  road- 
metal  than  those  of  the  lowan  or  Wisconsin  terraces,  as  their 
more  advanced  state  of  decay  permits  them  to  pack  well.  Pro- 
fessor Calvin  called  these  deposits  Buchanan  gravels  and  con- 
sidered them  as  having  been  deposited  as  the  Kansan  ice  sheet 
was  melting  away.  Since  they  occur  as  knolls  on  the  upland,  it 
appears  that  they  are  of  the  nature  of  kames.  Some  of  the  knolls 
are  thinly  mantled  with  younger  drift  (lowan). 


SUMMARY  OF  FACTS  REGARDING  GRAVELS  139 

COMPARISON  WITH   GRAVELS   OF  WISCONSIN  AGE. 

Wisconsin  valley-train  gravels  were  examined  somewhat  in 
Cerro  Gordo,  Floyd,  Franklin,  and  Hardin  counties.  The  amount 
of  leaching  of  these  is  much  less  than  in  those  of  the  lowan  ter- 
race gravels  and  other  alteration  is  less  also.  Limestone  pebbles 
occur  up  to  the  soil  or  within  two  feet  of  the  surface.  The  erosion 
of  the  Wisconsin  terraces  is  also  considerably  less.  There  can 
be  little  question  but  that  the  gravels  here  regarded  as  lowan 
are  older  than  those  washed  out  from  the  Des  Moines  lobe  of  the 
Wisconsin  stage. 

SUMMARY. 

The  chief  facts  which  were  noted  in  the  field  regarding  the 
gravel  phenomena  are : 

1.  Terraces  of  glacio-fluvial  gravel  occur  in  all  the  major 
valleys  in  the  lowan  area  and  continue  for  some  distance  beyond 
the  limit  of  the  lowan  into  the  Kansan  drift  area.    Those  in  the 
Wapsipinicon,  Maquoketa,  Volga,  Little  Turkey,  Turkey,  Upper 
Iowa,  Little  Cedar,  and  certain  smaller  valleys  have  no  other 
source  than  the  lowan  area, 

2.  So  far  as  noted  valleys  in  the  Kansan  area  which  do  not 
head  in  areas  of  younger  drift  do  not  contain  gravel  terraces. 

3.  The  sand  and  gravel  of  the  lowan  terraces  are  moderately 
weathered. 

4.  Some  small  gravel  knolls  occur  in  connection  with  local 
morainic  features  of  the  lowan  area.    The  materials  of  these  are 
weathered  similarly  to  the  lowan  terrace  gravels. 

5.  Here  and  there  in  the  lowan  drift  area  there    are    low 
rounded  knolls  of  much-decayed  gravels   (Buchanan).     These 
gravels  are  probably  of  Kansan  age.    Some  of  them  are  mantled 
with  the  later  drift. 

6.  The  lowan  gravels  are  considerably  more  weathered  and 
eroded  than  the  Wisconsin  gravels. 

These  facts  support  the  theory  that  an  ice  sheet  invaded 
northeastern  Iowa  at  a  time  considerably  later  than  the  Kansan 
and  some  time  prior  to  the  incursion  of  the  Des  Moines  lobe 
of  the  Wisconsin  ice  sheet. 


140  THE  IOWAN   DRIFT 

CHAPTER  VII 
THE  LOESS  AND  ITS  SIGNIFICANCE. 

One  cannot  work  in  the  area  of  the  lowan  drift  or  adjacent 
areas  of  older  drift  without  being  confronted  with  the  problem 
of  the  loess.  The  writers  did  not  undertake  an  exhaustive  study 
of  the  various  deposits  of  loess  but  some  observations  were 
made  which  have  direct  bearing  on  the  main  question  under  in- 
vestigation. Deposits  of  loess  known  to  be  of  pre-Iowan  or  of 
post-Wisconsin  age  are  not  included  in  the  following  discussion, 
excepting  as  specifically  indicated.  This  does,  however,  refer 
to  the  main  body  of  loess  in  the  Upper  Mississippi  valley  region. 

GENERAL   CHARACTERS. 

Earlier  students  have  shown  that  the  constituents  of  the 
main  body  of  loess  of  the  Upper  Mississippi  Valley  are  such  as 
would  be  derived  from  glacial  rock  flour,  that  is,  such  as  might 
be  blown  from  the  surface  of  the  drift  or  from  the  flood  plains 
of  valleys  draining  a  drift  area.37  The  loess  is  a  fine-textured, 
dustlike  silt,  buff  in  color  as  seen  in  most  shallow  exposures,  and 
gray  in  the  lower  parts  of  deeper  ones.  Generally,  when  rubbed 
between  the  fingers,  it  feels  floury.  From  this  it  varies  locally 
to  sandy  and  not  infrequently  is  it  found  closely  associated  with 
wind-blown  sand,  especially  in  the  lower  part.  There  are  also 
in  places  intercalated  layers  of  fine  sand.  The  writers  have 
not  observed  coarse  sand  or  pebbles  included  in  what  they  would 
regard  as  undisputed  loess.  In  parts  of  many  clean  exposures 
there  is  a  more  or  less  definite  banding  or  semblance  of  stratifi- 
cation, usually  conforming  to  the  surface  or  slope  on  which  the 
deposit  lies.  A  sort  of  flakiness  also  has  been  noted,  suggesting 
stratification,  but  clear-cut  lamination,  so  characteristic  of 
glaciolacustrine  silts,  is  rarely  if  ever  seen ;  so  also  definite  cross- 
bedding  is  comparatively  rare  and  such  as  is  seen  suggests 
eolian  rather  than  stream  deposition.  There  are  also  faint  dark 
colored  lines  here  and  there  which  may  be  the  residue  of  carbon 
from  vegetation  buried  during  the  deposition  of  the  loess. 

"Chamberlin,  T.  C.,  and  Salisbury,  R.  D.,  Preliminary  paper  on  the  driftless  area  of 
the  Upper  Mississippi  Valley:  U.  S.  Geol.  Survey  Sixth  Ann.  Kept.,  pp.  281-283,  304- 
305,  1885.  Chamberlin,  T.  C.,  Supplementary  hypothesis  respecting  the  origin  of  the 
loess  of  the  Mississippi  Valley:  Jour.  Geology,  Vol.  V,  pp.  794-802,  1897. 


FOSSIL  CONTENT  OF  THE  LOESS  141 

One  of  the  notable  characteristics  of  the  loess  when  it  is  dry 
is  vertical  cleavage  (Plate  VIII  B).  Unprotected,  nearly  verti- 
cal faces  will  stand  for  years  without  slumping  and  even  retain 
for  a  long  time  marks  of  the  excavator  or  "jack-knife  carved 
initial."  This  peculiarity  probably  results  from  homogeneity 
of  texture  and  interlocking  of  the  minute  angular  particles  of 
which  it  is  composed,  combined,  perhaps,  with  incipient  cementa- 
tion by  iron  oxide  or  calcium  carbonate  as  the  result  of  alternate 
wetting  and  drying. 

The  loess  bordering  and  overlapping  the  lowan  drift  area  is 
rarely  thicker  than  thirty  feet  and  in  most  places  there  is  less 
than  fifteen  feet. 

THE  FOSSIL  CONTENT  AND  ITS  SIGNIFICANCE. 

In  many  places  the  calcareous  part  of  the  loess  contains  small 
shells.  These  vary  in  size  from  tiny  spirals  to  shells  half  an 
inch  or  more  in  length.  In  some  places  they  are  numerous,  in 
others  moderately  so,  in  still  others  rare  or  absent. 

Professor  Bohumil  Shimek,  of  the  University  of  Iowa,  has 
made  an  extensive  study  of  the  character,  composition,  relations 
and  fossils  of  the  loess  and  has  published  his  results  in  a  long 
list  of  papers  covering  a  period  of  twenty-five  years.  The  chief 
points  of  significance  to  which  he  has  called  attention  in  these 
several  papers38  are:  (1)  the  shells  are  preponderantly  of  land 
snails;  (2)  they  are  identical  in  most  cases  with  those  of  snails 
now  inhabiting  damp,  shady  places  and  feeding  on  vegetation 
in  the  same  localities;  (3)  the  small  percentage  of  fresh-water 
forms  which  are  found  are  similar  to  those  which  now  live  in 
seepy  places  on  slopes  and  in  ponds;  (4)  many  of  the  shells  are 
fragile,  yet  generally  nearly  perfect  in  their  preservation. 

These  and  other  facts  as  to  texture,  composition,  geographic 
and  topographic  distribution  indicate,  according  to  Professor 
Shimek,  that  the  loess  was  deposited  by  wind,  that  the  sites  of 
deposition  were  clothed  with  vegetation,  and  that  the  climate 
was  much  like  the  present,  in  other  words  interglacial.  He 
writes  :39 

JSShirrek,  B.,  The  loess  and  the  Lansing  man:  Bull.  Lab.  Nat.  Hist.,  State  Univer- 
sity of  Iowa,  Vol.  V,  pp  327-346.  1899-1904.  Loess  and  the  lowan  drift:  Bull.  Lab. 
Nat.  Hist.,  State  University  of  Iowa.  Vol.  V,  pp.  352-367.  1899-1904.  The  significance 
of  Pleistocene  mollusks :  Soiree  (New  Ser.),  Vol.  XXXVII,  pp.  501-509,  1913. 

"Science,   N.   S.,  Vol.  XXXVII,  p.    508. 


142  THE  IOWAN   DRIFT 

The  only  conclusions  then  which  can  be  drawn  from 
the  fossils  of  the  loess  is  that  during  the  deposition 
of  the  several  loesses  climatic  conditions  were  not 
materially  different  from  those  which  exist  in  various 
parts  of  the  same  general  region  today.  Such  differ- 
ences as  do  exist  point  rather  to  a  drier  climate  in  the 
northern  part  of  the  loess-covered  area  than  that  of 
today. 

Since  no  plant  remains  have  been  found  in  the  loess,  he  argues 
that  the  rate  of  deposition  was  slow,  so  slow  that  the  generations 
of  trees  and  other  plants  had  time  to  decay  and  their  humus  resi- 
due to  be  dissolved  out  before  being  buried  to  depths  sufficient 
for  preservation. 

Most  of  the  foregoing  conclusions  seem  sound.  The  great 
predominance  of  land  shells  and  the  relative  scarcity  of  aquatic 
forms,  together  with  the  peculiarities  of  its  topographical  dis- 
tribution, have  had  considerable  influence  in  leading  many  to  an 
acceptance  of  the  eolian  theory  of  origin  of  the  loess.  It  is  not 
always  possible,  at  least  without  very  careful  study,  to  de- 
termine that  the  loess  at  any  given  exposure  has  not  been  modi- 
fied or  moved  since  its  original  deposition.  So  it  is  probable 
that  in  many  cases  some  of  the  textural  properties  of  the  loess 
as  seen  are  due  to  other  factors,  mainly  secondary,  such  as  re- 
handling  by  slope-wash,  creep  and  slump,  some  local  deposition 
in  transitory  ponds,  disturbance  by  burrowing  animals,  pene- 
trating roots,  and  uprooting  of  trees,  frost  action,  removal  of 
soluble  constituents  by  percolating  waters  and  their  redeposi- 
tion  as  layers,  concretions  or  tubules — that  all  of  these  and  per- 
haps others  have  contributed  to  its  present  physical  properties. 
With  allowance  made  for  such  factors  the  eolian  theory  of 
origin  for  the  loess  which  borders  and  overlaps  the  lowan  drift 
•seems  to  the  writers  to  meet  most,  if  not  all,  of  the  requirements 
of  the  case  if  a  source  of  the  material  is  available. 

MODIFICATION  OF  THE  LOESS  BY  WEATHERING. 

Wherever  thicknesses  of  eight  feet  or  more  of  loess  have  been 
seen  in  cuts  along  the  border  of  the  lowan  drift,  there  is  usually 
a  gradation  downward  from  leached  to  calcareous  loess  in  the 
lower  part.  A  few  feet  below  this  gradation  zone  the  loess 


RELATIONS  OF  THE  GI*AY  LOESS  143 

changes  color  from  buff  to  gray.    The  features  of  an  average 
exposure  are  given  in  the  following  generalized  section  : 

GENERALIZED  SECTION  OF  LOESS. 

Feet. 
3.     Soil,    black    humus,    changing   below    to    brownish,    no 


pebbles 

2.  Loess,  leached,  buff  to  yellow,  does  not  react  to  acid 
(dilute  HC1),  no  fossils  or  lime  concretions  in  this 
zone  ;  rarely  10-12  feet  ...............................  6-& 

1.  Loess,  calcareous,  upper  few  feet  buff,  grayish  below, 
includes  small  shells  and  calcareous  concretions  in 
many  places.  This  zone  is  usually  not  seen  in  exposures 
less  than  eight  feet  deep. 

The  persistence  of  these  general  characteristics  in  the  region- 
examined  by  the  writers  has  an  important  significance  in  read- 
ing the  history  of  the  loess.  Two  things  seem  to  be  indicated  by 
these  phenomena:  (1)  That  the  color  of  the  upper  ten  feet  or 
more  has  been  changed  by  oxidation  from  gray  to  buff  or  yel- 
lowish (and  to  brownish  just  below  the  soil)  ;  and  (2)  that  per- 
colating water  has  dissolved  and  removed  the  calcareous  par- 
ticles and  snail  shells  from  the  upper  six  to  eight  feet  or  more,. 
where  they  were  present.  If  the  calcareous  zone  is  not  exposed, 
fossil  shells  may  not  be  found. 

The  grayish  loess  has  been  regarded  by  some  as  a  dis- 
tinctly older  deposit  than  the  overlying  buff  loess.40  While 
this  may  be  true  of  some  of  the  gray  or  bluish  gray  loess  de- 
scribed by  Professor  Shimek  and  others  as  occurring  beneath 
the  buff  loess  in  places  outside  the  lowan  drift  area  the  writers 
have  seen  numerous  exposures  of  buff  loess  grading  downward 
into  gray  where  the  latter  shows  no  particular  evidence  of 
greater  age.  In  no  case  in  the  lowan  area  have  the  writers 
noted  any  zone  of  leaching  at  the  top  of  the  gray  loess  and  be- 
neath calcareous  buff  loess,  nor  has  such  a  definite,  highly  oxi- 
dized band  been  seen  separating  the  two  as  Professor  Shimek 
reports  having  seen  in  some  places.  The  writers  are  inclined  to 
regard  the  buff  and  the  gray  loess  seen  in  most  places  in  the 
northeastern  quarter  of  the  state  as  comprising  respectively 
the  oxidized  and  unoxidized  portions  of  one  practically  con- 
tinuous deposit.  The  general  absence  of  shells  and  other  cal- 
careous material  from  the  upper  six  to  eight  feet  or  more  of 

*>Shimek,  B.,  Loess  and  the  lowan  drift:  Bull.  Lab.  Nat.  Hist.  State  University  of: 
Iowa,  Vol.  V,  p.  366. 


144  THE   IOWAX   DRIFT 

the  loess,  would  seem  to  indicate  either  (1)  that  conditions 
during  the  time  of  deposition  of  this  upper  part  of  the  loess 
were  not  favorable  to  local  molluscan  growth  or  (2)  that  the 
time  since  has  been  long  enough  for  percolating  waters  to  dis- 
solve and  remoVe  the  shells  to  the  depths  indicated,  and  that 
the  deposition  of  this  loess  was  in  the  main  completed  some  time 
ago.  So  far  as  known  to  the  writers  there  is  no  evidence  war- 
ranting the  first  inference. 

Leaching  action  would  be  accomplished  by  oxidation  so  that 
if  the  second  deduction  be  correct  it  may  be  inferred  that  the 
loess  was  largely  unoxidized  and  gray  or  bluish  gray  in  color 
when  deposited.  In  those  places  where  deposition  of  loess  has 
continued  to  the  present  time  it  may  be  that  some  of  the  last 
of  the  transported  dust  was  derived  from  the  leached  and  oxi- 
dized portions  of  the  drift  and  alluvial  materials  and  so  was 
oxidized  and  noncalcareous  when  deposited  as  loess. 

The  above  phenomena  also  lead  one  to  the  inference  that  the 
main  mass  of  the  loess  was  once  calcareous,  that  whereas  now 
the  leached  zone  is  probably  increasing  in  depth  there  was  a 
time  when  calcareous  loess  accumulated  at  a  rate  greater  than 
the  rate  of  leaching.  These  inferences  strongly  suggest  a  special 
time  of  loess  deposition,  an  epoch  which  may  be  considered  as 
having  practically  closed  when  the  rate  of  deposition  became 
less  than  the  rate  of  leaching.  Since  then  there  has  probably 
been  relatively  little  loess  deposited  in  this  region  excepting 
locally  in  favored  situations. 

DISTRIBUTION  OF  THE  LOESS. 

The  loess  of  the  region  under  consideration  is  thickest  in  three 
situations:  (1)  along  river  valleys  draining  from  the  lowan 
drift  area;  (2)  around  the  border  of  the  lowan  drift,  and  (3) 
in  paha. 

(1).  In  some  places  the  buff  loess  and  associated  sand  is  so 
thick  bordering  the  larger  streams  as  to  form  hills  and  ridges 
rising  distinctly  above  the  adjacent  interstream  areas.  This  is 
so  noticeable  along  Cedar  river  in  Linn  and  Johnson  counties 
and  along  Wapsipinicon  river  in  Linn  and  Jones  counties  that 
one  is  reminded  of  the  remark  of  earlier  geologists,  that  the 
streams  left  the  plains  to  cut  through  the  hills.  An  exposure 


LOESS  ON  THE  IOWAN  DRIFT  MARGIN  145 

in  a  bluff  in  the  northwest  part  of  Cedar  Eapids  shows  the 
unusual  thickness  of  at  least  fifty  feet  of  loess,  and  at  the  Chi- 
cago &  North  Western  Eailway  quarry  southeast  of  that  city 
there  is  at  least  thirty  feet  of  loess  overlying  till  and  rock.  In 
some  instances  the  loess  in  such  situations  is  sandy. 

Besides  these  cases  of  conspicuous  topographic  effects,  there 
are  many  places  along  valleys  where  the  loess  is  thick  without 
forming  distinct  ridges,  and,  in  addition,  sand  dunes  are  to  be 
found.  The  thickening  of  the  loess  along  valleys  is  common 
both  within  and  without  the  lowan  drift  area,  probably  more 
so  outside  the  marginal  belt. 

Just  why  the  accumulation  of  loess  should  have  been  so 
marked  along  valleys  is  for  the  most  part  a  question  of  source 
of  supply  and  lodgment.  It  seems  reasonable  to  refer  the  source 
of  supply  in  large  part  at  least  to  the  river  flats  and  the  factors 
of  lodgment  to  vegetation  and  topography.  Northeastern  Iowa 
was  principally  a  prairie  region  at  the  time  of  settlement  by 
white  men,  the  timber  being  mostly  confined  to  belts  bordering 
the  streams,41  and  the  thicker  deposits  of  loess  are  found  mostly 
in  these  timbered  belts.  There  is  no  question  but  that  the 
arboreal  vegetation  would  favor  deposition  in  these  tracts.  The 
same  is  true  of  the  topography.  Not  only  would  the  steep  slopes 
and  ravines  cause  lodgment,  but  furthermore  the  reduction  of 
the  velocity  of  air  currents  sweeping  up  over  the  bluffs  from 
the  valley  bottoms  would  result  in  deposition  in  the  lee  of  the 
crests. 

(2)  Another  situation  where  the  loess  reaches  considerable 
thickness  is  around  the  border  of  the  lowan  drift  area.  It  has 
been  mentioned  that  the  till  within  this  area  is  generally  at  or 
near  the  surface,  and  that  on  crossing  the  border  to  the  area  of 
the  Kansan  drift  the  loess  covering  becomes  notably  thicker, 
even  in  locations  not  particularly  related  to  valleys.  As  dis- 
tance from  the  lowan  border  increases  the  thickness  of  the 
loess  on  the  Kansan  diminishes,  excepting  where  the  loess  is 
definitely  associated  with  valleys.  Over  most  of  the  lowan 
drift  area  loess  is  in  general  either  lacking  or  constitutes  a  very 


1  A3 


Kept.,  PI.  XXII,  1889-90. 
10 


146  THE   IOWAN   DRIFT 

thin  mantle  rarely  attaining  a  thickness  of  three  feet,  excepting 
in  the  southern  and  southwestern  parts  of  the  area,  in  Benton, 
Tama,  and  Grundy  counties,  where  thicknesses  of  four  to  six  feet 
are  common.  Reference  is  made  elsewhere  to  this  exceptional 
area. 

As  an  excellent  example  of  the  areal  relations  of  the  loess  to 
the  lowan  drift,  the  North  Liberty  plain  in  the  northern  part  of 
Johnson  county  may  be  cited.42 

This  plain,  which  is  four  to  five  miles  wide  and  about  eight 
miles  long,  appears  to  have  been  covered  by  an  extension  of  a 
lobe  of  the  lowan  ice  across  Iowa  river.  Its  longer  axis  trends 
northwest-southeast.  The  drift  here  is  covered  by  a  thin  mantle 
of  wind-blown  sand  and  loess  but  at  the  border  these  deposits 
thicken  abruptly  and  form  a  prominent  line  of  ridges  and 
hillocks  twenty  to  thirty  feet  high.  As  seen  from  the  North 
Liberty  plain  this  resembles  a  terminal  moraine  (Plate  IX). 
Exposures  and  auger  borings  in  this  belt,  however,  reveal  noth- 
ing but  loess  and  sand.  There  may,  perhaps,  be  a  low  core  of 
drift,  but  positive  evidence  of  such  is  wanting.  As  seen  from 
the  outer  side,  no  immediate  relief  is  discernible,  the  materials 
simply  spread  out  over  the  Kansan  drift  surface  and  mantle 
the  slopes  of  the  adjacent  valleys,  that  of  Iowa  river  on  the  east 
and  that  of  Clear  creek  on  the  south. 

The  ridges  on  the  south  and  southwest  sides  of  this  plain  are 
dominantly  sand,  but  beyond  these  the  texture  of  the  material 
changes  in  a  short  distance  to  that  of  loess  and  the  thickness  of 
the  deposit  is  less.  Cuts  on  the  Interurban  railway  near  the 
border  of  the  plain  which  are  twenty-five  feet  deep  do  not  reach 
the  bottom  of  the  loess,  whereas  shallow  road  cuts  five  miles  or 
less  outside  of  this  area  expose  the  underlying  Kansan  till. 
These  areal  relations  suggest  that  the  materials  of  the  border- 
ing ridges  were  blown  from  the  surface  of  the  plain  or  from  this 
and  its  westward  continuation,  the  broad  bottom  of  Iowa  river 
valley  in  northeastern  Iowa  county. 

Immediately  south  of  Blairstown,  in  southern  Benton  county, 
loess  is  thin  or  absent  from  the  area  having  the  lowan  type  of 

"Leighton,  M.  M.(  Iowa  Geological  Survey,  Vol.  XXV,  1916.  A  full  discussion  of 
the  evidences  that  the  North  Liberty  plain  is  a  part  of  the  lowan  drift  area  is  here 


THE  LOESS  OF  THE  NORTHEASTERN  BORDER         149 

topography,  but  it  thickens  abruptly  at  the  border  of  this  area 
and  mantles  the  rugged  eroded  surface  of  the  Kansan  drift  be- 
yond. If  the  loess  came  from  Iowa  river,  five  miles  to  the  south, 
why  should  it  thin  so  suddenly  at  the  boundary  of  the  area  hav- 
ing the  lowan  type  of  topography?  Possibly  because  the  drain- 
age conditions  of  the  dissected  Kansan  drift  controlled  the  dis- 
tribution of  the  timber  and  afforded  conditions  more  suitable 
for  anchorage  of  the  loess  than  did  the  smoothly  undulating 
prairie  farther  north.  On  the  other  hand  the  reason  may  be  that 
the  loess  was  blown  southward  from  the  raw  surface  of  the  newly 
deposited  lowan  drift  in  the  areas  which  continued  as  prairie. 
The  winds  may  have  been  anticyclonic,  blowing  from  the  sur- 
face of  the  retreating  ice  sheet  to  the  north  and  northwest. 

Within  that  part  of  the  northeast  border  of  the  lowan  drift 
area  which  extends  from  Fort  Atkinson  in  southwestern  Winne- 
shiek  county  to  Dyersville  in  western  Dubuque  county,  the 
lowan  till  is  generally  at  or  near  the  surface,  but  along  the 
border  the  loess  thickens  into  knolls  and  ridges.  Throughout 
much  of  this  distance  there  is  clearly  no  genetic  relation  between 
the  loess  border  and  any  streams.  There  is,  however,  a  close 
general  correspondence  between  this  border  and  the  line  be- 
tween prairie  on  the  west  and  timber  on  the  east,  as  shown  by 
McGee's  map.  In  other  words,  the  thickening  of  the  loess  along 
this  line  is  explainable  on  the  ground  that  the  forested  surface 
of  the  dissected  drift  to  the  east  afforded  adequate  anchorage 
for  the  wind-blown  material  but  one  must  look  elsewhere  than 
to  adjacent  valley  flats  for  the  places  of  derivation  of  the  dust 
by  prevailing  westerly  winds.  Professors  Chamberlin  and 
Salisbury,  in  their  study  of  the  Driftless  Area,  noted  that  this 
loess  thins  for  a  distance  eastward  and  then  thickens  again  in 
the  immediate  vicinity  of  Mississippi  river.43  A  correspond- 
ing change  in  texture  is  also  said  to  take  place,  there  being  a 
sandy  texture  along  the  lowan  border,  finer  farther  eastward, 
and  then  coarser  again  along  the  Mississippi.44  Professors 
Calvin,  Leonard,  Savage,  Udden,  and  Bain  in  their  reports  on 
the  counties  east  of  and  including  the  eastern  border  of  the 

«U    S    Geol.   Survey  Sixth  Ann.  Kept.,  p.   283,   1884-1885. 
"Ibid,  p.   281. 


150  THE   IOWAX   DRIFT 

lowan  drift  area45  refer  to  the  thickened  loess  along  this  border 
as  in  contrast  with  the  loess-free  area  to  the  west.  Thick- 
nesses are  stated  to  range  from  a  few  inches  to  thirty  feet. 
Professor  Leonard  states  that  the  average  thickness  in  Clayton 
county  is  not  over  ten  feet,  while  Udden  gives  the  average 
thickness  on  the  Kansan  drift  in  Clinton  county  as  fifteen  to 
twenty  feet.  All  refer  to  it  as  probably,  in  large  part  at  least, 
an  accumulation  of  dust  blown  from  the  lowan  drift  to  the  west. 

These  relations  certainly  strongly  suggest  that  the  loess  along 
the  east  border  of  the  lowan  drift  area  from  Winneshiek  county 
to  Dubuque  county  was  derived  from  the  surface  of  the  lowan 
drift.  Here  again  anticyclonic  winds  from  the  retreating  lowan 
ice  sheet  may  have  been  the  transporting  agent. 

(3)  Elliptical  hills  and  elongated  ridges  of  loess  or  capped 
with  loess,  which  McGee  called  paha,40  are  scattered  over  parts 
of  the  lowan  drift  area,  the  large  majority  of  them  being  con- 
centrated in  the  southeastern  part,  in  Benton,  Linn,  Johnson, 
and  Jones  counties.47  McGee48  included  in  the  type  of  topog- 
raphy represented  by  the  paha  "the  elongated  swell  of  soft 
and  graceful  contour,  standing  apart  on  the  plain  or  else  con- 
nected with  its  fellows  sometimes  in  long  lines,  again  in  con- 
geries, and  locally  merging  to  form  broad  loess  plateaus" 
(Plate  X).  A  few  are  situated  in  the  Kansan  drift  area,  but 
generally  not  far  from  the  lowan  border.  The  paha  of  the  lowan 
drift  area  are  situated  on  the  uplands,  and  in  most  cases  away 
from  valley  flats  so  that  it  is  probable  that  in  many  cases  the 
material  comprising  the  mantle  of  the  loess  and  sand  was 
blown  from  the  drift-plain  itself. 

One  of  the  most  notable  characteristics  of  these  hills  and 
ridges  is  the  prevalent  northwest-southeast  (south  45°  to  60° 
east)  trend  of  their  longer  axes. 

Their  persistent  southeasterly  trend  suggests  deposition  of 
the  loess  by  prevailing  northwesterly  winds,  possibly  anti- 
cyclonic  winds  blowing  from  the  retreating  ice  sheet.  There 
are,  however,  certain  reasons  for  suggesting  that,  in  some 

«Iowa  Geol.  Survey,  Vols.  IV,  V,  VIII,  X,  XIII,  XV,  XVI. 

"U.  S.   Geol.  Survey  Eleventh  Ann.   Kept.,   pp.   220.   255.   396-414,   446-459,   1889-90. 

47See  S'tanwood,  Fairfax,   Rock  Island,   Cordova,   Farley  and  Winthrop   topographic 

"Op.  Cit.,  p.  397. 


FROM  U.  S.  G.S.  TOPOGRAPHIC  MAPS 

(ANAMOSA  AND  MECHANICSV1LLE  SHEETS,  IOWA) 


IOWA  GEOLOGICAL  SURVEY 
PLATE  X 


TOPOGRAPHIC  MAP  OF  A  PORTION  OF  THE  IOWAN  DRIFT  PLAIN 
IN  LINN  AND  JONES  COUNTIES,  IOWA,  SHOWING  PAHA 


Scale    62*500 


Contour  Interval  20  feet 
Datum,  is  mean*  Sea,  LeyeL 


THE  LOESS   OF  THE  PAHA  151 

instances  at  least,  the  direction  of  the  wind  was  transverse 
rather  than  parallel  to  this  trend,  that  is  southwesterly,  and 
that  the  trend  itself  is  due  to  the  orientation  of  drumloidal  till 
cores. 

Till  was  seen  by  the  writers  exposed  up  to  thirty  feet  above 
the  base  of  the  eighty-foot  north  slope  in  the  road  cut  on  the  paha 
ridge  three  miles  northwest  of  Lowden,  Cedar  county.  Above 
this  level  the  cut,  which  was  ten  to  fifteen  feet  deep,  was  wholly 
in  loess  to  the  top  of  the  ridge. 

Another  hill,  which  would  probably  be  classed  as  a  paha, 
stands  two  miles  north  of  Sand  Spring,  Delaware  county.  It  is 
about  one-half  mile  long,  less  than  one-fourth  mile  wide,  and  its 
slopes  rise  sharply  from  the  flat  plain  to  a  height  of  about  fifty 
feet.  Its  long  axis  trends  slightly  south  of  east.  A  road  cut 
at  the  crest  of  the  ridge  exposed  seven  feet  of  buff  loess  over- 
lying four  feet  of  leached  till  (apparently  Kansan)  with  a  well- 
marked  red  ferretto  zone  at  the  top. 

Professor  Wm.  H.  Norton  in  his  reports  on  the  Geology  of 
Linn,49  Scott,  Cedar,  and  Bremer  counties  presented  consider- 
able evidence  showing  that  some  at  least  of  these  hills  have  cores 
of  glacial  till  and  he  discusses  the  question  of  the  nuclear  till 
hills  being  genetically  related  to  drumlins  or  other  forms  due  to 
the  moving  ice.  He  cites  the  paha  in  Cedar  county  as  found  in 
three  areas. 

*  *  *  an  area  peripheric  to  the  lowan  frontier,  in  part 
within  the  lowan  drift,  and  in  part  situated  on  the  Kansan  over- 
looking the  lowan  plains  below,  and  an  area  upon  the  Kansan 
too  remote  from  the  lowan  border  to  have  been  under  the  con- 
trol of  the  glacier  ice  of  that  invasion. 

Although  most  of  the  paha  are  in  the  lowan  drift  area  and 
have  been  regarded  by  several  writers  as  in  some  way  related 
to  the  lowan  stage  of  glaciation  they  are  not  wholly  confined 
to  this  area  and  as  noted  above  the  nuclei,  in  some  cases  at 
least,  appear  to  be  Kansan  till. 

Under  the  eolian  hypothesis,  drumlins  of  Kansan  or  lowan 
drift,  or  of  both,  as  well  as  other  hills,  would  afford  suitable 

*»Iowa  Geological  Survey  Vol  IV,  pp.  177-184,  1894;  Vol.  IX.  395,  1898;  Vol. 
XI.  PP  356-36^  1900  ;  VoT' XVI."  pp. '376-386,  1905.  See  also  T  E.  Savage's  report 
on  Beaton  county  for  description  of  till  nuclei :  Iowa  Geological  Survey,  Vol.  XV,  pp. 
141-143. 


152  THE   IOWAN   DRIFT 

places  for  lodgment  of  wind-blown  dust,  both  because  of  their 
own  relief  and  because  in  many  instances  they  were  probably 
covered  with  timber.  If  the  nuclei  of  the  paha  really  are 
drumloidal  the  prevalent  trend  is  explained  as  the  long  axes  lie 
parallel  to  the  known,  or  probable  directions  of  the  ice  move- 
ment. The  thickness  of  the  loess  capping  is  in  numerous  cases 
fifteen  or  twenty  feet  or  more. 

Among  the  sections  of  paha  examined  by  the  writers  were  the 
cuts  in  the  Norway  paha  described»by  Professor  Savage50  where 
there  seems  clearly  to  be  a  till  core  to  the  ridge.  The  beauti- 
fully striated  limestone  bowlder  pictured  by  McGee51  as  from 
the  loess  of  the  Norway  paha  probably  came  originally  from  the 
till  core  of  the  ridge  and  was  introduced  into  the  loess  by  rolling 
or  sliding  down  the  hill  slope  while  the  loess  was  accumulating 
about  it,  though  McGee  did  not  so  explain  its  presence.  Writing 
of  the  foreign  materials  in  the  loess  in  this  connection  McGee 
states : 

Foreign  materials  are  rarely  found  within  it;  in 
perhaps  one  in  twenty  of  the  sections  commonly  exposed  in  rail- 
way or  roadway  cuttings,  cellar  excavations,  and  roadside 
gullies,  bowlder-like  masses  of  drift  clay,  ranging  from  an  inch 
to  a  foot  or  two  in  diameter,  may  be  found;  in  one  section  in 
a  hundred  an  erratic  pebble  (generally  well  rounded)  may  ap- 
pear; in  one  section  in  five  hundred- a  bowlder  a  foot  or  more 
in  diameter  may  be  found;  and  in  one  section  of  the  many 
thousands  examined  a  limestone  bowlder,  so  beautifully  striated 
as  admirably  to  illustrate  this  class  of  icework,  came  to  light. 

Probably  in  most,  if  not  all,  cases  the  occurrence  of  pebbles 
or  bowlders  in  the  loess  can  be  explained  in  a  manner  similar  to 
that  given  above. 

One  relation  of  sand  and  loess  to  an  included  bowlder  was 
very  well  illustrated  in  a  cut  on  the  interurban  electric  railway, 
one  mile  northwest  of  Bertram,  Linn  county,  Iowa  (Township 
83  North,  Range  6  West,  north  line  of  the  northeast  quarter  of 
section  33)  (figure  13).  The  section  showed: 

Towa  Oeol.  Purvey,  Vol.  XV.  r.   142. 

^U.  S.  Geol.  Survey    Eleventh  Ann.  Kept.,  PI.  XLVI. 


THE  SOURCES  OP  THE  LOESS 


153 


Fig.  13. — Diagram  of  drift  exposed  on  electric  railway  near  Bertram,  Iowa,  showing 
relations  of  till  (1  and  2),  'wind-blown  sand  (3),  and  loess  and  soil  (4), 
to  an  included  etched  and  polished  bowlder  (5). 


DRIFT  NORTHWEST  OF  BERTRAM. 

Feet. 

4.     Loess,   buff-brown    3± 

3.    Alternating   buff   sand   and   brown   clayey   sand   stratified, 
with  cross-beds  dipping  eastward,  wind-blown 5 

2.  Till,  sticky,  brown,  pebbly,  noncalcareous  clay 3± 

3.  Till,  dense,  dark  slate-colored,  highly  calcareous 10+ 

Lying  on  the  surface  of  the  weathered  till  (No.  2)  and  em- 
bedded in  No.  3  was  a  bowlder  of  coarse-grained  red  granite 
about  three  feet  in  diameter,  whose  sides  and  upper  surface 
were  etched  and  polished  as  by  a  sand  blast.  This  sand  was 
probably  blown  from  the  broad  bottom  of  Cedar  river  about  one 
mile  to  the  southwest. 

Conclusion  as  to  the  sources  of  the  loess.— From  the  foregoing 
considerations  it  appears  probable  that  the  sources  of  supply 
of  the  loess  in  and  adjacent  to  the  lowan  drift  area  were  in  some 
cases  the  valley  flats,  in  others  the  lowan  drift  plain.  The 
writers  do  not,  however,  extend  this  interpretation  to  the  loess 
of  southern  and  western  Iowa  and  adjacent  parts  of  Missouri, 
Kansas,  and  Nebraska,  not  wishing  to  express  in  this  con- 
nection an  opinion  as  to  the  sources  of  the  loess  of  these  more 
distant  areas. 


154  THE   IOWAN   DRIFT 

STRATIGRAPHIC  RELATIONS  OF  THE  LOESS. 

Relations  to  the  Kansan  drift. — In  the  Kansan  area  the  loess 
mantles  the  slopes  as  well  as  the  uplands,  showing  clearly  that 
the  Kansan  drift-plain  was  dissected  before  the  loess  was  de- 
posited. There  are  also  numerous  sections  which  show  this 
unconformity  in  another  way;  calcareous  and  fossiliferous  loess 
overlies  highly  weathered  Kaiisan  drift.  This  is  well  shown 
by  the  relations  in  the  cut  near  the  west  end  of  the  interurban 
railway  bridge  west  of  Iowa  City.  Here  approximately  thirty 
feet  of  buff  loess,  leached  of  calcium  carbonate  to  a  depth  of 
about  ten  feet,  and  calcareous  and  fossiliferous  below,  rests 
on  nine  feet  of  thoroughly  leached,  highly  oxidized  and  partly 
decomposed  Buchanan  gravel,  which  lies  in  a  sag  on  reddish 
leached  Kansan  till.  The  buff  loess  at  its  base  grades  into  some- 
what coarser,  noncalcareous  reddish  material  which  may  have 
been  swept  from  the  red  soils  of  adjacent  surfaces  of  Buchanan 
gravel  or  Kansan  drift. 

Widespread  over  the  Kansan  drift  area  south  and  east  of 
the  lowan  drift  plain,  a  red  soil  or  ferretto  is  found  underlying 
the  loess  where  these  are  exposed  in  many  railroad  and  high- 
way cuts.  In  the  new  Chicago,  Milwaukee  &  St.  Paul  railway 
cuts  near  Melbourne  in  Marshall  county,  near  Vining  in  Tama 
county,  and  east  of  Delmar  Junction  in  Clinton  county,  the  loess 
overlies  the  ferretto  and  the  eroded  surface  of  the  Kansan 
drift. 

Calcareous  loess  overlying  noncalcareous  super-Kansan 
"gumbo"  has  already  been  cited  (See  also  Plate  XI).  The 
story  told  by  this  relation  is  the  same  as  that  read  from  the  fore- 
going relations.  In  fact  the  evidence  throughout  the  loess- 
covered  Kansan  drift  area,  from  Marshall  and  Jasper  counties 
on  the  west  to  Mississippi  river  on  the  east,  and  from  Clinton 
county  on  the  south  to  the  Minnesota  line  on  the  north,  shows 
that  a  long  period  of  weathering  and  erosion  intervened  be- 
tween the  deposition  of  the  Kansan  till  and  that  of  the  loess 
under  consideration. 

Relations  to  the  Illinoian  drift. — The  loess  is  continuous 
across  the  Kansan  drift  to  the  Illinoian  area  in  southeastern 


RELATIONS  OF  THE  LOESS  TO  THE  ILLINOIAN  TILL  155 

Iowa,  and  mantles  the  Illinoian  drift.  An  examination  of  the 
deposit  at  many  points  in  Scott,  Muscatine,  Louisa  and  Des 
Moines  counties  shows  it  to  have  practically  the  same  constitu- 
tion and  amount  of  modification  by  weathering  as  the  loess 
farther  north. 

Cuts  on  the  Davenport  and  Muscatine  interurban  railroad 
through  upland  divides  four  miles  west  of  Davenport,  expose 
twelve  to  twenty  feet  of  buff  loess,  leached  to  depths  of  seven 
or  eight  feet,  and  calcareous  and  fossiliferous  below.  There 
is  a  mantle  of  loess  even  on  the  flat  upland  which  generally  is 
thicker  than  the  eight-foot  auger  could  penetrate.  In  most 
places  it  is  leached  at  least  eight  feet,  but  in  one  or  two  instances 
calcareous  loess  was  struck  at  six  to  seven  feet.  In  a  few  other 
places  northeast  and  northwest  of  Davenport,  the  thickness  of 
noncalcareous  loess  noted  ranged  from  five  to  eighteen  feet.  In 
the  area  west  of  Muscatine,  buff  loess,  with  a  leached  zone  simi- 
lar to  that  of  the  loess  immediately  bordering  the  lowan  drift 
area,  mantles  the  Illinoian  drift  to  depths  of  more  than  eight 
feet.  The  same  is  true  about  Wapello,  and  also  west  and  north 
of  Burlington,  excepting  that  in  the  latter  locality  the  loess  is 
slightly  thinner.  Here  no  thicknesses  greater  than  five  to  seven 
feet  were  noted,  and  in  most  cases  it  is  leached  throughout  its 
entire  thickness. 

Examinations  of  the  loess  by  Mr.  Alden  in  the  Illinoian  drift 
area,  in  parts  of  Rock  Island,  Henry,  McDonough,  and  Fulton 
counties,  Illinois,  showed  the  prevalence  of  similar  character- 
istics as  to  thickness,  composition,  fossil  content,  and  amount 
of  modification  by  weathering.  This  deposit  is  continuous  east- 
ward to  and  across  Illinois  river  where,  as  shown  by  Mr. 
Leverett,52  it  passes  under  the  early  Wisconsin  drift  in  the 
region  of  Peoria.53 

While  the  loess  lying  on  the  Illinioan  till  is  apparently  of 
the  same  age  as  that  overlapping  the  lowan  drift,  it  seems  clear 
that  the  Illinoian  till  suffered  much  more  modification  by 
weathering  and  erosion  prior  to  the  deposition  of  the  loess  than 
did  the  lowan  drift.  This  is  discussed  in  the  following  chapter. 

"Illinois  elacial  lobe,  U.  S.  Geol.  Survey  Mono.   38,  p.   187,   1899. 

"In  places  along  the  Mississippi  bluffs  there  was  observed  light  gray  to  light 
buff  loess  which  is  leached  to  a  depth  of  but  two  to  four  feet.  This  may  be  the 
product  of  later  eolian  deposition,  continuing  to  the  present. 


156  THE  IOWAN   DRIFT 

Relations  to  the  loivan  drift. — In  the  area  of  the  lowan  drift 
the  loess  is  generally  so  thin  that  the  leached  zone  extends  down 
into  the  till.  None  of  the  exposures  or  borings  revealed  cal- 
careous loess  overlying  leached  till.  On  the  other  hand,  at  least 
one  section,  in  an  interurban  railroad  cut  near  Lisbon,  Linn 
county,  exposed  calcareous  till  immediately  beneath  calcareous 
loess  and  sand.  The  relations  noted  at  this  place  were  as  fol- 
lows: 

DBIFT  WEST  OF  LISBON,  IOWA. 

Feet. 

Loess,  leached    6 

Loess,  calcareous  2-3 

Sand    1-2 

Till,   calcareous 2-3 

Eelations  similar  to  these  were  found  by  making  borings  in 
the  southwestern  part  of  the  lowan  drift  area,  in  Benton,  Tama, 
and  Grundy  counties.  The  loess  in  this  latter  territory  is  thicker 
than  in  the  rest  of  the  lowan  area,  and  lies  as  a  general  mantle 
with  an  average  thickness  of  four  to  six  feet.  In  penetrating 
this  again  and  again  with  the  auger,  it  was  found  that  the  loess 
was  wholly  leached  but  that  the  till  beneath  was  rarely  leached 
more  than  a  few  inches  to  one  and  one-half  feet.  In  other  words, 
where  the  covering  of  loess  on  the  lowan  drift  is  thicker  the 
leaching  of  the  till  is  less.  This  strongly  suggests  that  the 
leaching  process  has  but  recently  reached  the  till.  The  absence 
of  any  deeper  color  due  to  oxidation  of  the  upper  part  of  the 
till  as  compared  with  the  color  of  the  overlying  loess  is  of  like 
significance.  It  indicates  that  the  lowan  till  suffered  but  little 
modification  by  weathering  before  the  loess  was  deposited 
upon  it.  There  is  generally  at  the  top  of  the  till  and  beneath 
the  loess,  as  seen  in  cuts,  a  more  or  less  definite  line  of  pebbles. 
This  is  probably  the  residual  coarse  material  left  from  the  slight 
wind  erosion  and  rain  wash  which  occurred  at  those  particular 
places  before  the  till  was  protected  by  the  loess. 

In  line  with  the  foregoing  evidences  is  the  fact  that  no  soil 
was  seen  between  the  loess  and  the  underlying  till  in  the  area  of 
the  lowan  drift  such  as  was  observed  in  the  Illinoian  drift  area 
in  the  vicinity  of  Wapello  and  Burlington.  Moreover,  the 
lowan  till,  where  not  loess-covered,  is  leached  to  somewhat  less 


RELATIONS  OF  THE  LOESS  TO  THE  IOWAN  TILL  157 

depths  than  the  average  sections  of  loess  in  the  bordering 
Kansan  drift  area.  This  is  in  harmony  with  the  textures  of  the 
two  formations.  Since  the  loess  is  more  porous  than  the  till, 
it  should  show  a  greater  depth  of  leaching  if  both  are  of  ap- 
proximately the  same  age. 

All  these  considerations  of  the  character  and  relations  of  the 
loess  lead  to  the  conclusion  (1)  that  a  very  long  time  intervened 
between  the  disappearance  of  the  Kansan  ice  sheet  and  the 
deposition  of  the  main  sheet  of  loess  under  discussion,  (2)  that 
there  was  also  a  considerable  interval  after  the  Illinoian  ice 
melted  away  before  the  Illinoian  drift  became  mantled  with 
loess,  and  (3)  that  on  the  contrary,  the  deposition  of  this  loess 
followed  almost  immediately  the  recession  of  the  front  of  the 
glacier  which  laid  down  the  lowan  drift. 

This  conclusion  may  at  first  seem  incompatible  with  the 
presence  of  'the  fossil  shells  which,  according  to  Professor 
Shimek,  are  like  those  species  of  snails  which  live  in  the  same 
region  today  and  feed  upon  vegetation.  It  should  be  recognized, 
however,  that  the  climate  at  the  close  of  a  glacial  epoch 
is  probably  different  from  that  at  the  beginning.  The  for- 
mation and  extension  of  a  glacier  is  a  consequence  of 
glacial  conditions  having  prevailed  for  some  time.  Its  develop- 
ment and  advance  are  preceded  first  by  a  change  to  glacial 
temperatures  and  a  vast  accumulation  of  snow.  The  retreat 
of  the  ice  front,  on  the  other  hand,  occurs  only  when  the  inter- 
glacial  climate  has  become  well  established.  Probably  a  zone 
adjacent  to  the  retreating  front  of  a  continental  ice  sheet  is 
affected  by  cold  winds  blowing  from  its  surface  and  somewhat 
by  the  presence  of  the  ice  itself,  but  the  conditions  are  less 
severe  than  in  the  case  of  an  advancing  ice  sheet.  In  the  former 
case,  the  climate  opposes  the  existence  of  the  ice,  while  in  the 
latter,  it  is  responsible  for  it.  Although  present  temperatures 
probably  did  not  prevail  in  the  immediate  vicinity  of  the  lowan 
ice,  it  seems  likely  that  after  the  climate  had  so  changed  that  the 
ice  had  melted  back  hundreds  of  miles  from  its  extreme 
limit,  seasons  approximating  those  of  the  present  may  have 
prevailed  over  those  areas  where  the  loess  now  occurs.  The 
length  of  time  consumed  in  a  retreat  of  even  a  thousand 


158  THE   IOWAN   DRIFT 

miles  would  be  brief  geologically,  and  probably  would  not 
have  resulted  in  any  conslerable  amount  of  weathering  of 
the  new  drift.  The  statement,  therefore,  seems  sound,  that 
the  main  sheet  of  loess  under  consideration  was  deposited  im- 
mediately following  the  lowan  stage  of  glaciation.  It  is  there- 
fore a  near-correlative  of  the  lowan  drift,  though  it  really  rep- 
resents the  early  part  of  the  Peorian  stage  of  deglaciation. 

Relations  to  the  Wisconsin  drift. — If  the  conclusion  is  sound 
that  most  of  the  loess  in  and  adjacent  to  the  lowan  area  was 
deposited  immediately  following  the  lowan  stage  of  glaciation, 
the  main  deposit  of  loess  should  be  found  extending  beneath 
the  Wisconsin  drift. 

No  sections  were  observed  by  the  writers  in  Worth,  Cerro 
Gordo  or  Franklin  counties  showing  either  the  lowan  drift  or 
the  overlying  loess  extending  westward  under  the  late  Wiscon- 
sin drift  of  the  Des  Moines  lobe.  Neither  have  such  exposures 
been  reported  by  the  Iowa  Geological  Survey.  No  thorough 
search  for  such  was  made  by  the  present  writers  nor  was  there 
any  extended  examination  of  the  Wisconsin  drift.  A  few  short 
trips  were  made  across  the  border  in  the  last  three  of  the  coun- 
ties named.  In  most  of  the  places  seen  there  was  no  loess  on 
the  Wisconsin  drift.  In  a  few  places  in  Franklin  a  thin  coating 
of  loess  or  loesslike  loam  was  found  on  the  marginal  slope  of  the 
Wisconsin  drift  while  thicknesses  of  one  to  ten  feet  were  found 
quite  generally  on  the  lowan  drift  to  the  east.  At  one  point 
six  miles  southwest  of  Ackley,  Hardin  county  (near  middle 
of  south  one-half  of  Aetna  township,  Township  89  North,  Eange 
19  West),  in  the  area  of  the  Wisconsin  drift,  a  boring  was  made 
which  penetrated  leached  loess  four  and  one-half  feet  and  cal- 
careous loess  three  and  one-half  feet  without  reaching  the  under- 
lying till.  This  is  probably  a  rather  exceptional  deposit  blown 
up  from  Iowa  river  about  one  mile  distant.  On  the  lowan  drift 
plain  to  the  east  thicknesses  of  one  to  eight  feet  were  observed, 
the  lower  part  being  calcareous  where  the  thickness  was  greater 
than  four  to  four  and  one-half  feet. 

These  are,  of  course,  not  the  first  observations  of  slight  local 
deposits  of  loess  overlying  Wisconsin  drift.5*  Similar  occur- 

"Salisbury,  R.  D.,  Loess  in  the  Wisconsin  drift  formation.  Jour.  Geology,  Vol.  4, 
pp.  929-938,  1896. 


THE  LOESS  AND  THE  WISCONSIN  TILL  161 

rences  have  been  noted  by  Mr.  Leverett  at  various  places  in 
Illinois55  and  by  Mr.  Alden  at  various  places  in  southern  Wis- 
consin and  in  Bureau  County,  Illinois. 

Shimek  has  described  post- Wisconsin  loess  also  and  has 
shown  that  some  loess  deposition  has  continued  to  the  present 
time  and  is  yet  going  on.  These  deposits  of  known  Wisconsin 
or  post-Wisconsin  age  should  not,  however,  lead  to  confusion  of 
the  discussion  in  hand,  which  is  that  the  loess  formerly  called 
"lowan"  but  deposited  during  the  Peorian  stage  of  deglaciation, 
extends  beneath  the  Wisconsin  drift. 

In  southeastern  Hardin  county  and  in  Marshall  county  the 
lowan  drift  does  not  extend  westward  to  the  Wisconsin  drift 
boundary  but  the  loess  is  continuous  across  the  interval  and 
passes  beneath  the  later  drift.  In  his  report  on  the  geology 
of  Hardin  county56  Prof.  S.  W.  Beyer  wrote  as  follows : 

Outcrops  of  the  loess  may  be  observed  well  across  Providence 
township,  and  the  loess  undoubtedly  continues  under  the  Wis- 
consin drift  and  connects  with  the  deposits  near  Ames  in  Story 
county.  On  the  southeast  quarter  of  section  6  in  Providence 
township  the  loess  appears  in  a  cut  along  the  roadway  overlain 
by  twenty  feet  of  Wisconsin  drift  and  resting  upon  the  oxidized 
Kansan.  Also  in  section  16,  in  a  road  cut,  eight  feet  of  loess  is 
visible.  The  deposits  at  these  exposures  are  closely  set  with 
root  casts,  some  of  which  measure  four  inches  in  diameter.  Loess 
concretions  are  numerous  and  a  few  gasteropod  shells  were 
noted,  the  most  common  being  a  species  of  Succinea. 

At  a  point  about  twenty-seven  miles  south  of  the  Hardin 
county  exposure,  the  writers  found  similar  relations  exhibited 
by  a  cut  on  the  Chicago,  Milwaukee  &  St.  Paul  railway  in  the 
northwest  quarter  of  section  19,  Eden  township  (Township  82 
North,  Eange  20  West),  Marshall  county.  At  this  place,  which 
is  about  three  miles  southwest  of  Rhodes,  the  railway  climbs 
from  the  dissected  area  of  the  Kansan  drift  to  the  Wisconsin 
drift  plain.  The  big  cut  at  the  county  line  (Plate  XI)  showed 
the  following  section : 

"Leverett,    F.,    The    Illinois   glacial    lobe,    U.    S.    Geol.    Survey    Mon.    38,    pp.    267-268, 

99 

MBeyer,  S.  W.,  Geology  of  Hardin  County:  Iowa  Geol.  Survey,  Vol.  X,  p.   282,  18&9. 


11 


1899, 


162  THE   IOWAN   DRIFT 

DRIFT  i.\   CHICAGO,   MILWAUKEE  &  ST.   PAUL  RAILWAY   CUT  THREE 
MIIES  SOUTHWEST  OF  RHODES,  IOWA. 

Feet. 

4.     Till,  Wisconsin,  leached  three  feet,  calcareous  below 25 

3.     Loess,  mostly   buff,  gray  at  bottom,   leached  four  or  five 

feet  in  one  place,  snail  shells  in  calcareous  portion 25 

2.     "Gumbo,"  noncalcareous  gray  clay,  similar  to  that  found 

elsewhere  on  the  Kansan  drift,  contains  small  pebbles 8-10 

1.     Till,    probably    Kansan,    brownish    buff,    contains    rotten 

granites,  leached  9-10  feet,  calcareous  below ;_  exposed 5-12 

Aii  irregular  ferruginous  line  or  shell  two  to  three  inches  thick 
extends  obliquely  through  part  of  the  loess  and  ends  at  the  base 
of  the  Wisconsin  till  as  though  cut  off. 

Here  it  is  clear  that  the  loess  was  deposited  not  only  before 
the  late  Wisconsin  ice  invasion,  but  at  a  time  separated  there- 
from by  an  interval  of  leaching  and  oxidation  (the  Peorian 
interglacial  stage  of  Leverett). 

As  noted  above  (page  155)  Mr.  Leverett  has  shown  that  the 
loess  also  extends  eastward  beneath  the  early  Wisconsin  drift 
in  the  region  of  Peoria,  Illinois. 

SUMMARY  OF  THE  RELATIONS  OF  THE  LOESS. 

1.  The  loess  in  and  about  the  lowan  drift  area  is  believed 
to  be  mostly  wind-blown  material. 

2.  The  sources  of  supply  were  in  some  cases  the  surface  of 
the  lowan  drift,  in  others  the  valley  flats  both  within  and  outside 
of  the  lowan  area. 

3.  It  is  probable  that  this  loess  was,  for  the  most  part,  origi- 
nally calcareous. 

4.  If  it  was  originally  calcareous,  that  part  which-  was  blown 
from  the  surface  of  the  lowan  drift  must  have  been  derived 
before  the  drift  was  leached.    This  is  one  reason  for  regarding 
its  age  as  immediately  post-Iowan  or,  in  other    words,    early 
Peorian.    This  is  in  agreement  with  the  evidence  showing  that 
the  lowan  drift  was  but  little  eroded  or  modified  by  weathering 
prior  to  the  deposition  of  the  loess. 

5.  The  Kansan  drift  area  was  probably  already  clothed  witli 
vegetation  when  the  accumulation  of  this  loess  began,  as  is  in- 
dicated by  the  presence  of  herbivorous  land-snails  in  the  loess. 
The  change  from  a  glacial  to 'an  interglacial  climate,  which  had 
already  initiated  the  retreat  of  the  lowan  ice  front  made  such 


GENERAL,  RELATIONS  OF  THE  LOESS  163 

vegetation  possible.  This  vegetation,  especially  the  arboreal, 
was  a  factor  in  affording  lodgment  for  the  loess,  as  was  also  the 
rough  topography  of  the  Kansan. 

6.  The  recently  exposed  surface    of    the    lowan    drift    un- 
doubtedly had  some  vegetation  soon  after  the  melting  of  the  ice, 
but  it  was  probably  sparse.     There  is  nothing  to    show    that 
arboreal  vegetation  ever  gained  much  of  a  foothold  in  the  lowan 
drift  area  excepting  in  the  rougher  parts  and  in  narrow  belts 
along  the  streams. 

7.  The  broad  prairies,  when  they  were  dry  and  where  they 
were  not  effectively  protected  by  prairie  grasses,    were    un- 
doubtedly sources  for  clouds  of  dust  and    sand,    just    as    the 
ploughed  fields  of  man  and  his  unpaved  highways  have  been 
since  his  appearance. 

8.  The  till  nuclei  of  the  paha  rising  above  the  surrounding 
plain  were  well  drained  and  favored  the  growth  of    arboreal 
vegetation  and  thus   afforded  increased  lodgment  for   eolian 
materials. 

9.  In  order  that  the  loess  could  have  accumulated  as  a  cal- 
careous deposit,  the  rate  of  deposition  must  have  exceeded  the 
rate  at  which  the  calcium  carbonate  was  removed  by  leaching. 
It  is  therefore  perhaps  not  incorrect  to  say  that  there  was  a 
special  time  of  deposition  for  the  loess  which  borders  and  over- 
laps the  lowan  drift.     This  is  particularly  so  since  there  was 
time  for  considerable  leaching  and  oxidation  of  that  part  of 
this  loess  which  now  underlies  Wisconsin  till  before  that  later 
till  was  deposited. 

10.  The  time  of  main  loess  deposition  probably  did  not  end 
abruptly,  but  as  vegetation  more  completely  covered  the  drift, 
the  amount  of  material  blown  about  by  the  winds  gradually 
diminished. 

11.  Although  the  time  of  main  loess  deposition  is  thought 
to  have  been  short,  geologically  speaking,  it  is  probable  that  the 
rate  of  accumulation  of  the  loess  even  during  that  time  was 
sufficiently  slow  for  successive  generations  of  plants  to  decay 
before  the  vegetable  matter  was  buried  to  such  depths  as  to  be 
preserved. 


164  THE   IOWAX   DRIFT 

CONCLUSIONS  FROM  THE  RELATIONS  OF  THE  LOESS. 

The  general  conclusions  from  this  study  of  the  loess  are  those 
stated  above  (page  157) ;  (1)  that  the  deposition  of  the  upper- 
most till  of  the  lowan  drift  area  occurred  but  a  short  time  prior 
to  the  accumulation  of  the  main  sheet  of  loess  which  borders  arid 
overlaps  it;  (2)  that  the  Illinoian  till  was  deposited  at  a  time 
considerably  before  this  epoch  of  loess  deposition,  and  (3)  that 
the  Kansan  drift  was  deposited  considerably  earlier  than  the 
Illinoian  till  and  much  earlier  than  the  loess  was  formed,  or 
in  other  words,  this  line  of  evidence  also  supports  the  view  that 
the  lowan  stage  of  glaciation  was  distinct  from,  and  later  than, 
either  the  Kansan  or  Illinoian  stages  of  glaciation. 


CHAPTER  VIII 
THE  AGE  OF  THE  IOWAN  DRIFT. 

Considerable  evidence  has  already  been  presented  tending 
to  show  that  the  lowan  drift  is  distinct  from  and  younger  than 
the  Kansan  drift.  The  amount  of  modification  of  the  drift  by 
weathering  and.  the  stratigraphic  relations  of  the  main  deposit 
of  loess  show  clearly  that  the  lowan  drift  is  also  distinct  from 
and  older  than  the  Wisconsin  drift.  The  lowan  drift  is  not  now 
known  to  extend  into  the  area  covered  by  the  Illinoian  ice  sheet 
nor  to  overlap  the  Illinoian  drift,  so  that  their  mutual  age  rela- 
tions can  not  be  determined  directly  but  must  be  inferred  from 
comparison  of  the  relative  amounts  of  their  modification  by 
weathering  and  erosion  and  by  their  relations  to  the  main  de- 
posit of  loess.  Eeference  has  been  made  to  these  relations  in 
the  preceding  chapters  and  the  characteristics  of  the  lowan 
drift  have  been  discussed  at  length.  The  Illinoian  drift  has 
been  treated  by  Mr.  Leverett  in  his  monograph.57  Some  further 
consideration  may  be  given  to  it  in  this  connection. 

In  southeastern  Iowa  and  in  that  part  of  western  Illinois 
south  of  Rock  river  which  was  examined  by  Mr.  Alden,  the  Illi- 
noian drift  area  has  a  fairly  uniform  type  of  topography.  The 
striking  features  are  the  broad  upland  areas  (in  many  places 

"Leverett,  Frank,  The  Illinois  glacial  lobe:  U.   S.  Geol.  Survey  Mon.  38,  1899. 


WEATHERING  OF  THE  ILLINOIAN  TILL  167 

four  to  five  miles  wide)  and  the  sharply  incised  valleys  (Plate 
XII).  The  uplands  are  nearly  flat,  and ''comprise  relatively 
much  more  area  than  do  the  remnants  of  the  Kansan  upland 
in  Iowa  (Plate  I).  The  larger  valleys  average  100  to  150  feet 
in  depth,  and  have  valley  flats  one-half  to  one  mile,  or  rarely  two 
miles  wide.  Branching  tributaries  have  partly  dissected  the 
bordering  uplands,  but  on  the  whole  they  are  short  (Plate  XIII). 
The  broad,  flat  upland  tracts  with  the  sharply-cut  valleys  in- 
tervening, give  the  impression  that  the  Illinoian  ice  on  melting 
left  a  nearly  flat  drift  plain.  Since  then  sufficient  dissection 
has  taken  place  to  develop  drainage  systems  to  a  stage  of  late 
youth. 

As  compared  with  the  lowan  drift  topography  (Plate  II)  the 
Illinoian  shows  considerably  more  erosion.  In  some  parts  of 
the  Illinoian  drif.t  area  this  may  be  due  partly  to  proximity  to 
Mississippi  river,  which  has  resulted  in  fairly  high  .gradients.58 
But  on  the  other  hand,  the  original  surface  of  the  Illinoian 
drift  probably  was  nearly  flat,  whereas  the  surface  of  the  lowan 
drift  originally  had  gentle  slopes,  with  inherited  major  drainage 
lines.  The  latter  condition  is  thought  to  be  as  favorable  to  the 
development  of  a  drainage  system  as  the  former,  if  not  more 
so;  and,  hence,  the  greater  amount  of  erosion  of  the  Illinoian 
drift  appears  to  indicate  a  longer  time  of  exposure.59 

The  weathering  of  the  upper  part  of  the  Illinoian  till  was  due 
to  its  exposure  prior  to  the  deposition  of  the  loess.  The  oxidized 
zone  is  not  generally  cut  off  by  the  erosional  slopes  as  is  the 
f  erretto  at  the  top  of  the  Kansan  but  it  extends  well  down  below 
the  upland  where  the  slopes  are  not  too  steep.  The  loess  also 
mantles  the  slopes 'at  least  part  way  down  where  these  are  steep, 
and  entirely  to  the  bottom  where  they  are  not  so  steep.  Most 
of  the  erosion  and  oxidation  of  the  Illinoian  till  thus  appears  to 
have  been  accomplished  prior  to  the  deposition  of  the  loess. 


168  THE   ICWAX   DRIFT 

There  seems  to  have  been  comparatively  little  erosion  since  the 
loess  was  laid  down. 

Near  Davenport,  Iowa,  in  the  cuts  above  referred  to,  the  loess 
lies  on  slopes  of  erosion  of  the  Illinoian  and  older  tills,  and  the 
calcareous  and  fossilif erous  portion  of  the  loess  rests  on  till  oxi- 
dized to  a  brownish  tint  and  leached  to  depths  of  about  six 
feet.  In  the  vicinity  of  Wapello,  Iowa,  there  are  exposures 
showing  a  buried  soil  separating  the  loess  from  till,  and  in  some 
places  a  "  gumbo  "-like  clay  is  found  at  this  horizon.  In  Grand- 
view  township  (Township  75  North,  Kange  3  West)  south  line 
of  the  southeast  quarter  of  section  33,  there  was  exposed  in  both 
sides  of  a  ravine  the  following : 

DEPOSITS  FOUR  AXD  ONE-HALF  MILKS   NORTH  OF  WAPELLO.   IOWA. 

Feet. 
2.     Loess,  buff,  rusty  at  bottom 12 

1.  Silt,    almost    black    like    soil    at    top,    dark    drab    below, 
"gumbo"-like  in  texture,  with  scattered  small  pebbles  and 
sand   grains,    noncalcareous 5-  6 

In  Port  Louisa  township  (Township  74  North,  Kange  3 
West),  north-central  part  of  section  10,  a  road  cut  on  a  valley 
slope  showed : 

DEPOSITS  THKEE  AXD  OXE-HALF  MILES  NORTH  OF  WAPELLO,  IOWA. 

Feet. 

2.  Loess,  buff,  rusty  at  bottom 10 

1.     Soil  ( contact  sharp) ,  exposed 1 

At  neither  of  these  places  was  the  underlying  till  exposed. 

Some  of  the  more  deeply  weathered  till  exposed  in  these 
counties,  especially  in  cuts  well  below  the  upland  level,  may  be 
Kansan.  At  these  places  the  Illinoian  till  is  .absent  beneath  the 
loess,  apparently  as  the  result  of  preloess  erosion,  and  if  the 
weathered  zone  is  absent,  it  is  not  always  possible  without  care- 
ful examination  to  determine  whether  the  till  exposed  is  Kansan 
or  Illinoian.  Where  moderately  weathered  till  is  exposed  at 
the  higher  levels  the  presumption  is  that  it  is  Illinoian.  Pro- 
fessor Udden  found  a  lithologic  difference  between  the  Kansan 
and  Illinoian  till  of  this  region  but  the  writers  made  no  such 
careful  comparison. 

In  1905,  Mr.  Alden  examined  an  exposure  in  Wapello  town- 
ship, (Township  74  North,  Eange  3  West,  northwest  quarter  of 


GUMBO  ON  THE  ILLINOIAN  TILL  169 

section  15),  in  the  face  of  the  bluff  east  of  the  north  end  of  the 
Iowa  river  bridge.  When  seen  in  1914  the  section  was  badly 
obscured  by  slumping  but  peat  and  soil  could  still  be  seen  be- 
neath twenty-five  feet  of  loess  and  sand.  The  section  when  seen 
in  1905  showed  the  following  deposits : 

SECTION-  OF  IOWA  RIVEB  BLUFF  Two  AXD  ONE-HALF  MILES  NORTH  OF 
WAPELLO,  IOWA. 

Feet.     In. 

11.     Sand,  stratified    10.i5 

10.     Loess,   buff   to   gray 10 

9.     Loess  and  sand,  interstratified ..'.'.'.     '.     5-6 

8.     Humus,  dark    i_  ji/ 

7.     Peat  containing  fragments  of  trees 8 

6.     Humus,  black  to  grayish 4 

5.     Sand,  yellowish  gray,  obscured ? 

4.     Clay    (till?),    leached,    jointed,    mottled    reddish 
gray  to  bluish  gray,  speckled  in  upper  part  with 

light  spots  and  bright  blue  spots 1142 

3.     Clay,  rusty,  oxidized Q.  3 

2.     Clay,  ashen  gray  ; ...  S_IQ 

1.     Sand,  fine,  stratified  10 

Talus. 

Udden  describes  the  Sangamon  soil,  which  separates  the 
Illinoian  till  from  the  overlying  loess,  as  well  developed  at  many 
places  in  Louisa  county.  The  peaty  phase  is  said  to  be  most 
pronounced  in  the  east  bluffs  along  Iowa  river  northeast  of 
Wapello. 

North  of  Burlington,  soil  and  gray  "gumbo"  were  seen  be- 
neath the  loess  in  Burlington  township  (Township  70  North, 
Range  2  West),  west  line  of  section  4;  in  Franklin  township 
(Township  71  North,  Range  3  West),  southeast  quarter  of  sec- 
tion 13;  and  in  Yellow  Springs  township  (Township  72  North, 
Range  3  West),  central  part  of  section  32.  Borings  made  by 
the  writers  on  the  flat  upland  near  the  south  line  of  section  2, 
Franklin  township,  and  in  Flint  River  township  (Township  70 
North,  Range  3  West)  at  the  middle  of  the  north  line  of  sec- 
tion 2,  revealed  a  black  soil  beneath  about  seven  feet  of  loess. 
In  the  former  place  the  lower  three  and  one-half  feet  of  the 
loess  was  gray  and  calcareous.  In  this  county,  as  in  the  others, 
the  loess  mantles  the  slopes  as  well  as  the  uplands. 

Doctor  Kay60  states  that  "after  a  somewhat  careful  study  of 
the  gumbo  which  lies  on  the  Illinoian  drift  in  southeastern  Iowa, 

""Kay,  Geo.  F.,  Gumbotil,  a  new  term  in  Pleistocene  geology :  Science,  new  ser., 
Vol.  XLIV,  pp.  637-638,  1916. 


170  THE  IOWAN  DRIFT 

and  which  was  discussed  by  Lever ett  in  Monograph  XXXVIII 
of  the  United  States  Geological  Survey,  pages  28  to  33,  the 
conclusion  has  been  reached  that  here,  also,  the  gumbo  is  so  re- 
lated to  the  drift  that  it  is  undoubtedly  the  thoroughly  weathered 
product  of  the  Illinoian  drift." 

Mr.  Leverett  has  discussed  the  Sangamon  soil  and  weathered 
zone  as  developed  in  Illinois.61  He  describes  one  extensive  ex- 
posure of  the  soil  as  found  at  the  Brick  and  Tile  Works  in 
Galva  (Henry  county).  Here  fifteen  feet  of  loess  is  underlain 
by  one  foot  of  black  mucky  soil  in  which  was  embedded  a  log  one 
foot  in  diameter.  Beneath  this  was  the  Illinoian  till. 

Mr.  Alden  also  observed  the  loess  in  similar  relations  to  the 
weathered  and  eroded  drift  in  that  part  of  Illinois  lying  south 
of  the  big  bend  of  Mississippi  river  and  the  Green  river  basin, 
although  only  slight  traces  of  black  soil  were  noted  by  him  at 
the  Sangamon  horizon. 

From  these  various  observations  it  is  evident  that  the  Illinoian 
drift  has  been  modified  much  more  by  weathering  and  erosion 
than  has  the  lowan.  It  also  appears  that  most  of  the  modifica- 
tion of  the  Illinoian  occurred  prior  to  the  formation  of  the  main 
deposit  of  loess.  It  seems  clear  therefore  that  the  lowan  drift 
is  entirely  distinct  from  and  considerably  younger  than  the 
Illinoian  drift.  At  the  Illinoian  stage  of  glaciation  the  Labrador 
ice  sheet  extended  to  and  across  Mississippi  river  in  south- 
eastern Iowa.  The  relations  of  the  Keewatin  glacier  at  that 
time  are  not  known.  During  the  Sangamon  stage  of  deglacia- 
tion  the  Illinoian  drift  was  considerably  eroded,  its  upper  part 
was  leached  and  oxidized,  soil  and  vegetable  deposits  were 
formed  and,  in  places,  a  super-Illinoian  ' '  gumbo ' '  was  developed. 
This  was  followed  by  the  extension  of  an  ice  sheet  from  the 
Hudson  Bay  region  southward  into  northeastern  Iowa  and  the 
deposition  of  the  lowan  drift.  The  relations  of  the  Labrador 
glacier  at  this  stage  are  not  now  known.  Accompanying  and 
following  the  melting  of  the  lowan  ice  prevailing  conditions 
resulted  in  the  accumulation  of  the  main  deposit  of  loess.  This 
represents  the  early  part  of  the  Peorian  stage  of  deglaciation. 
During  the  later  part  of  this  stage  the  Peorian  soil  and  weath- 

•"Leverett,  F.,  The  Illinois  glacial  lobe:  U.  S.  Geol.  Survey  Mon.  38,  pp.  125-130, 
1899. 


LIMITS  OP  THE  IOWAN  DRIFT  171 

ered  zone  was  developed  and  the  loess  and  lowan  till  were 
subjected  to  some  erosion,  leaching  and  oxidation.  This  stage 
of  deglaciation  was  followed  by  an  extension  of  the  ice  from  both 
the  Labrador  and  Keewatin  centers,  that  from  the  latter  over- 
riding the  lowan  drift  excepting  in  northeastern  Iowa  and, 
perhaps,  in  southeastern  Minnesota  and  some  areas  farther 
west.  At  one  of  the  oscillations  of  the  Keewatin  ice  sheet  of 
the  Wisconsin  stage  the  Des  Moines  lobe  occupied  north-central 
Iowa.  On  its  melting  the  Recent  epoch  was  inaugurated.  The 
consideration  of  the  various  lines  of  evidence  reviewed  in  this 
paper  leads  the  writers  to  the  conclusion  stated  in  the  Introduc- 
tion, that  there  is  warrant  for  the  continued  use  of  lowan  drift 
and  lowan  stage  of  glaciation  as  major  subdivisions  of  the 
Pleistocene  classification. 


CHAPTER  IX 
BORDER  PHENOMENA  AND  LIMITS  OF  THE  IOWAN  DRIFT. 

It  seems  necessary  to  make  some  statement  concerning  the 
definition  of  the  limits  of  the  lowan  drift.  It  should  be  under- 
stood, however,  that  but  little  work  was  done  by  the  present 
writers  on  either  the  determination  of  the  exact  limits  of  this 
drift  sheet  or  on  the  verification  or  revision  of  the  boundaries 
as  previously  mapped.  The  time  devoted  to  the  field  work  was 
spent,  for  the  most  part,  in  the  study  of  the  broader  questions 
involved.  Owing  to  the  similarity  in  lithologic  composition  of 
the  lowan  and  the  Kansan  drifts,  as  'noted  above  and  as  shown 
by  the  tabulated  results  of  pebble  counts  (Tables,  Appendix  A) 
and  the  paucity  of  terminal  morainal  phenomena,  it  would  prob- 
ably be  difficult  if  not  impossible  to  determine  accurately  in 
detail  the  present  limits  of  the  lowan  drift.  In  a  general  way 
the  border  can  probably  be  approximately  located  as  at  or  near 
the  places  where  the  undissected  and  mantled  topography  of 
the  lowan  area  gives  way  to  the  dissected  topography  charac- 
teristic of  the  older  drift.  'The  drift  is  probably  generally  thin 
and  doubtless  it  has  been  removed  by  erosion  from  the  more 
dissected  tracts  bordering  the  main  streams.  It  seems  to  the 


172  THE  IOWAN   DRIFT 

writers  that  the  line  shown  on  the  published  maps  is 
rather  the  inner  limit  of  the  thicker  parts  of  the  loess  than  the 
actual  outer  boundary  of  the  lowan  drift,  either  as  at  present 
preserved  or  as  originally  deposited.  While  there  is  not  a 
great  deal  of  loess  in  the  lowan  area,  the  lowan  drift  and  the 
loess  are  probably  not  in  reality  so  nearly  mutually  exclusive 
as  was  originally  supposed.  As  indicated  above  (Chapter  VII), 
there  is  in  many  places  a  certain  amount  of  loess  overlying  the 
lowan  drift.  On  the  other  hand  there  are  some  neighboring 
areas  showing  little  or  no  loess  which  the  lowan  ice  may  not 
have  covered. 

A  portion  of  the  northeastern  border  of  the  lowan  drift  is 
fairly  well  defined,  and  at  intervals  along  this  border  there  is 
a  mild  development  of  morainal  phenomena.  Five  miles  south- 
west of  Ridgeway  (Sumner  township,  -Township  97  North, 
Range  10  West)  a  tract  was  observed  showing  morainal  knolls. 
When  the  tops  of  two  of  these  were  dug  into,  gravels  were 
exposed.  About  a  mile  west  of  Fort  Atkinson  (Washington 
township,  Township  96  North,  Range  9  West,  section  7)  knolls 
of  drift  sprinkled  with  bowlders  and  pebbles  mark  the  border 
of  the  lowan.  They  appear  to  be  banked  at  the  head  of  a 
tributary  of  Turkey  river.  With  these  is  a  limestone  hill  forty 
feet  high. 

Three  miles  east  of  Ridgeway,  on  K.  P.  Kuntson's  farm,  in 
Winneshiek  county,  in  section  20  of  Madison  township,  there  is 
a  moraine,  trending  a  little  north  of  west.  The  line  of  hillocks 
rises  as  much  as  forty  feet -above  the  nearly  flat,  upland  plain 
to  the  south.  The  area  to  the  north  is  deeply  dissected.  A 
gravel  pit  fifteen  feet  deep  in  one  of  the  hillocks  shows  it  to  be 
a  kame.  The  material  is  rather  coarse,  partly  water-worn 
gravel  which  ranges  from  sand  to  cobbles  six  to  eight  inches  in 
diameter,  though  it  averages  one-half  inch  to  one  and  one-half 
inches.  It  is  cross-bedded,  with  a  dip  as  high  as  30  degrees. 
An  estimate  of  the  percentages  of  the  various  kinds  of  rock-types 
made  by  counting  and  sorting  pebbles  shows  the  following: 


IOW AN  DRIFT  IN  FAYETTE  COUNTY  173 

Per  Cent  Per  Cent 

Limestone    32  Quartz     2 

Granite     15  chert 

Greenstone    26  Sandstone    2 

Quartzite    15  Porphyry    1 

Dolerite    4  ironstone   1 

Total   103 

Some  of  the  limestone  pebbles,  as  well  as  some  of  the  others, 
have  a  slight  rusty  and  black  coating.  Incipient  cementation  is 
present,  but  so  little  that  with  the  stroke  of  the  hammer  the 
gravel  falls  freely.  As  a  result  of  leaching  the  upper  five  feet 
are  barren  of  limestone  pebbles. 

Some  low  moraine-like  knolls  appear  to  mark  the  lowan  border 
near  Conover.  A  cut  and  boring  show  the  presence  of  till.  The 
nearby  kettle-like  depression  may  really  be  a  limestone  sink 
and  not  a  glacial  kettle-hole. 

In  the  northeastern  part  of  Howard  county  there  is  a  belt  of 
swells,  but  so  far.  as  they  were  seen  the  knolls  appeared  to  be 
of  loess  and  not  morainal.  The  same  is  true  in  southeastern 
Orleans  township,  "Winneshiek  county. 

Two  to  three  miles  south  of  Conover,  the  head  of  a  tributary 
of  Youngs  creek  appears  to  be  blocked  with  drift.  A  well  here 
shows  the  presence  of  forty  feet  of  drift,  though  drift  is  very 
thin  to  the  eastward.  It  is  probable  that  the  lowan  ice  extended 
somewhat  east  of  this  drift  ridge  down  the  broad  open  swales 
that  lead  to  the  upper  terrace  or  second  plain  which  is  so  well 
developed  in  this  region.  The  outwash  gravels  extend  into  and 
through  the  inner  gorge,  which  is  here  cut  eighty  feet  or  more 
below  this  upper  terrace  level. 

IiTthe  northern  part  of  Windsor  township,  Fayette  county 
(Township  94  North,  Range  9  West),  five  or  six  miles  north- 
west of  WTest  Union,  a  moraine-like  ridge  lies  along  the  border 
of  the  lowan  area  as  mapped.  Some  small  sags  occur  with  the 
knolls.  A  cut  and  boring  in  one  of  the  swells  showed  seven  feet 
of  leached  till  over  calcareous  till;  another  cut  exposed  only 
loess. 

Two  to  three  miles  southeast  of  West  Union  (Union  township, 
Township  94  North,  Eange  8  West,  sections  27  and  28,  and  also 
in  section  32)  there  are  ridges  and  knolls  at  the  lowan  border. 


174  THE   IOWAN   DRIFT 

It  is  possible  that  some  of  these  are  of  loess  but  others  are 
certainly  of  drift. 

Along  the  lowan  border  between  Fayette  and  Arlington  are 
numerous  low  knolls.  Some  of  these  are  of  gravel,  others  are 
of  loess  or  loess-mantled  drift.  It  is  in  this  belt  not  more  than 
two  or  three  miles  southeast  of  Fayette  that  excavation  for  the 
railway  cuts  exposed  the  two  tills  with  intercalated  forest  bed 
which  are  cited  by  McGee.62 

The  main  road  from  Strawberry  Point  to  Edgewood  in 
southwest  Clayton  county  follows  a  well-defined  ridge  which 
marks  the  border  of  the  lowan  area.  Cuts  expose  ten  to  fifteen 
feet  of  loess,  but  most  of  the  bulk  of  the  ridge  is  probably  of 
till.  Eecords  of  several  wells  show  thicknesses  of  100  to  200 
feet  of  clay  above  the  limestone. 

Some  knolls  occur  southeast  of  Edgewood.  In  section  8 
Bremen  township  (Township  89  North,  Bange  3  West)  a  ridge 
of  gravel  knolls  rises  sharply  in  true  morainal  fashion  thirty 
to  forty  feet  above  the  surrounding  land.  The  gravels  are, 
however,  oxidized  brownish  and  considerably  decomposed  (about 
as  much  as  the  Buchanan  gravel).  Gravels  which  are  exposed 
two  to  three  miles  farther  west,  in  Oneida  township  (Township 
89  North,  Bange  4  West,  section  12,  west  line),  are  less  deeply 
weathered. 

There  may  be  some  question  as  to  whether  or  not  the  lowan 
ice  really  extended  farther  southeast  and  south  of  this  point 
in  the  area  east  of  Maquoketa  river  and  south  of  the  Illinois 
Central  railroad  in  the  southeast  part  of  Delaware  county. 
While  the  topography  of  the  narrow  upland  plain  between 
Dyersville  and  Farley  closely  resembles  in  part  that  of  the 
typical  lowan  plain,  the  relations  of  the  drainage  between  Dyers- 
ville and  Farley  are  somewhat  anomalous,  and  the  amount  of 
weathering  of  the  drift  exposed  and  of  that  penetrated  in  sev- 
eral borings  is  greater  than  that  commonly  noted  on  the  lowan. 
The  writers  have  therefore  some  doubt  as  to  the  lowan  ice 
having  extended  beyond  Dyersville.  East  of  Farley  the  erosion 
lines  sharpen  immediately  north  and  south  of  the  narrow  up- 
land strip.  No  calcareous  material  was  found  in  the  drift  here 

CZU.  S.   Geol.    Survey   Eleventh   Ann.    Kept.,   pt.   1,    p.    487-489. 


IOWAN  DRIFT  IN  DUBUQUE  COUNTY  175 

within  eight  to  fourteen  feet  of  the  surface.  Although  in  nu- 
merous places,  the  limestone  outcrops  or  is  but  thinly  covered, 
there  is  some  thick  drift.  A  well  on  the  Onstreide  farm  (New 
Wine  township,  Township  89  North,  Range  2  West,  section  35, 
southeast  quarter),  about  two  miles  northwest  of  Farley,  is  re- 
ported to  have  penetrated  115  feet  of  drift.  Apparently  there 
is  here  a  buried  valley  as  the  present  drainage  lines  are  cut 
into  limestone  not  far  away.  The  shifting  of  drainage  here  may 
account  for  the  lack  of  dissection. 

While  the  writers  have  not  examined  the  area  of  the  supposed 
Worthington-Barnard  lobe  except  for  parts  near  Worthington, 
it  appears  from  study  of  the  published  description,  the  topo- 
graphic maps,  and  field  notes  of  Mr.  Leverett  and  Professor 
Chamberlin,  that  there  is  little  real  basis  for  mapping  this  as 
having  been  occupied  by  a  lobe  of  the  low  an  ice.  The  distribu- 
tion of  the  bowlders  and  of  the  loess  does  not  seem  to  the  writers 
to  define  the  limits  of  the  lowan,  while  the  topographic  relations 
render  such  a  lobate  extension  inherently  improbable.  Doctor 
Calvin  and  some  of  the  other  observers  appear  to  have  reached 
the  same  conclusion.  While  there  are  considerable  tracts  of 
smooth,  nearly  flat,  topography  resembling  the  topography  of 
the  lowan  area  south  of  the  Illinois  Central  railway,  other  parts, 
as  southeast  of  Delhi,  are  greatly  dissected.  Eough  weathered 
limestone  is  exposed  (often  in  projecting  ledges)  at  numerous 
places  and  the  till  where  seen  is  considerably  weathered.  In 
some  places  it  is  not,  however,  more  weathered  than  the  known 
lowan.  One  hill,  in  this  area,  the  sharp  forty-foot  ridge  two 
miles  north  of  Sand  Spring  (South  Fork  township,  Township 
87  North,  Range  3  West,  sections  9  and  10),  is  quite  clearly  built 
of  Kansan  drift,  as  the  road  in  the  crest  exposes,  beneath  seven 
feet  of  loess,  the  well-marked  red  ferretto  of  the  top  of  the 
Kansan  till. 

Two  or  three  miles  northeast  of  Sand  Spring  is  a  moraine- 
like  belt  of  hills.  The  gravels  exposed  in  a  pit  in  one  of  these 
hills  (South  Fork  township,  Township  87  North,  Range  3  West, 
section  11,  southwest  quarter)  are  much  weathered.  Lime- 
stone pebbles  are  mostly  absent  from  the  upper  part  of  the 
fifteen-foot  section  as  they  have  been  removed  by  solution  ex- 


176  THE   IOWAN   DRIFT 

cepting  some  deeply  etched  blocks  on  the  surface.  Limestone 
pebbles  are  present  lower  down  but  some  are  so  badly  de- 
composed as  to  crumble  to  powder  in  the  fingers.  Granites 
crumble  under  the  hammer ;  greenstones  have  rusted  exteriors ; 
clay  ironstones  have  formed,  and  pebbles  are  much  coated  with 
iron  oxide,  manganese  dioxide  or  calcium  carbonate.  If  the 
lowan  ice  really  did  extend  into  this  area  these  gravels  may 
perhaps  be  regarded  as  part  of  its  terminal  moraine.  They 
may,  however,  be  older. 

If  the  lowan  ice  extended  onto  the  upland  west  of  Cascade,  it 
is  difficult  to  see  how  it  could  have  avoided  occupying  the  valley 
of  Maquoketa  river,  yet.  the  constricted  winding  gorge  below 
Monticello  with  vertical  cliffs  and  castellated  towers  of  lime- 
stone shows  the  characteristics  of  the  Driftless  Area  rather 
than  a  valley  so  recently  glaciated.  It  seems  probable  that  the 
ice  did  not  extend  farther  down  than  the  head  of  this  gorge  near 
Monticello.  The  writers  have  also  some  doubt  as  to  all  of  the 
gently  undulating  strip  of  country  which  extends  from  Monti- 
cello  and  Langworthy  southeast  to  Onslow,  having  been  glaciated 
at  this  time.  The  drift  in  this  tract  varies  from  one  foot  or  less 
to  260  feet  or  more,  as  shown  by  the  records  of  wells.63  Its  un- 
dissected  topography  is  apparently  due  to  the  results  of  stream 
shifting  by  the  Kansan  ice  sheet.  While  the  Maquoketa  was 
forced  to  entrench  itself  in  the  rock  but  a  short  distance  to  the 
north,  the  surface  configuration  of  this  belt  caused  half  of  this 
area  to  drain  in  a  reverse  direction  to  the  main  stream  at  Monti- 
cello  and  this  course  has  led  the  little  brook  across  outcropping 
rock  ledges.  Both  factors  have  retarded  dissection;  the 
eastern  part  drains  east  to  the  main  stream  but  this  has  also 
been  retarded  by  cutting  in  limestone.  The.  pre-Kansan  or 
preglacial  drainage  was  probably  southward  to  Wapsipinicon 
river,  but  a  big  drift  ridge  now  lies  athwart  this  course.  It 
seems  to  the  writers  probable  that  the  margin  of  the  lowan  ice 
lay  across  the  plain  somewhere  east  of  Langworthy,  but  that  it 
did  not  extend  so  far  east  as  Onslow. 

The  drift  ridge  indicated  extends  northwest  from  Wyoming 
past  Amber  toward  Prairieburg.  As  shown  on  page  93  there 

'  ;l".  S.  Geol.  Survey  Water-Supply  Paper,  No.  293,  p.  437-441,  1912.  Iowa  Geol. 
Survey,  Vol.  XXI,  pp.  528-532,  1912. 


IOWAN  DRIFT   IN   JONES   COUNTY  177 

is  good  evidence  that  the  lowan  ice  overrode  this  ridge  south- 
eastward to  a  point  about  a  mile  beyond  the  line  of  the  Chicago, 
Milwaukee  &  St.  Paul  Eailway.  This  is  shown  by  the  smoothed- 
out  contours  of  the  ridge  farther  northwest  and  by  the  presence 
on  top  of  the  ridge  south  of  Langworthy  of  thin  lowan  drift 
overlying  the  super-Kansan  soil  and  ' '  gumbo. ' '  Farther  south- 
east the  ridge  is  much  dissected,  the  glacial  till  is  deeply  weather- 
ed, and  such  traces  of  the  "gumbo"  as  have  been  found  have 
no  overlying  later  drift.  It  therefore  seems  probable  that  the 
margin  of  the  lowan  ice  lay  across  this  ridge  not  far  east  of  the 
line  of  the  Chicago,  Milwaukee  &  St.  Paul  Eailway.  South  of 
this  it  must  have  occupied  the  valley  of  Wapsipinicon  river, 
though  the  valley  slopes  show  little  or  no  evidence  of  its  presence. 

From  the  latitude  of  Anamosa  southward  to  Iowa  river  in 
Johnson  county  there  is  such  an  alternation  of  smoothly  un- 
dulating plains  and  loess  covered  hilly  tracts  together  with  the 
dissected  belts  bordering  the  Wapsipinicon,  Cedar  and  Iowa 
rivers,  that  there  is  considerable  ground  for  difference  of  opinion 
as  to  just  what  areas  were  covered  by  the  lowan  ice.  It  is, 
indeed,  doubtful  whether  any  two  observers  working  wholly 
independently  would  reach  similar  conclusions.  The  presence 
of  rather  low,  gently  undulating,  undissected  tracts  of  consider- 
able size,  with  here  and  there  a  big  granite  bowlder  and  even  with 
till  but  moderately  weathered  leads,  on  the  one  hand,  to  the 
mapping  of  a  long  lobe  extending  fifty  or  sixty  miles  southeast- 
ward from  the  main  lowan  area  to  the  Mississippi  near  Clinton. 
On  the  other  hand,  the  inherent  improbability  of  the  extension 
of  a  lobe  of  any  such  length  and  with  so  small  a  width  (only 
eight  or  ten  miles  in  southern  Jones  and  northern  Cedar  coun- 
ties), makes  one  hesitate  to  consent  to  any  such  mapping 
especially  when  the  relative  elevations  of  this  and  adjacent  tracts 
are  considered. 

There  is  little  or  no  evidence  as  to  the  relations  of  the  ice 
front  to  the  Wapsipinicon  valley  above  and  below  Anamosa.  The 
slopes  are  sharply  dissected  and  loess-mantled.  At  the  few 
places  where  till  was  seen  by  the  writers  it  showed  considerable 
evidence  of  weathering,  such  as  the  red  ferretto  zone  of  the 
Kansan.  Whatever  lowan  drift  was  deposited  on  these  slopes 
12 


178  THE   IOWAN   DRIFT 

has  probably  been  removed  by  subsequent  erosion  or  covered  by 
the  loess. 

It  has  been  supposed  that  the  margin  of  the  lowan  ice  extended 
from  the  vicinity  of  Olin  in  southern  Jones  county,  southeast- 
ward along  the  south  border  of  the  loess-mantled  hills  which  lie 
south  of  the  Wapsipinicon  between  Olin  and  Massilon.  These 
hills  appear  to  be  of  Kansan  drift  mantled  with  eight  to  ten 
feet  of  loess.  The  belt  south  of  the  Wapsipinicon  between  the 
Chicago,  Milwaukee  &  St.  Paul  and  the  Chicago  &  North  Western 
railway  lines,  has  in  part  a  gently  undulating  topography  of  the 
lowan  mantled  type,  for  example  north  of  Stan  wood  and  Clar- 
ence. In  large  part,  however,  it  is  occupied  by  hills  which,  so 
far  as  is  known,  are  principally  of  Kansan  drift  with  a  moder- 
ately thick  coating  of  loess.  Those  with  the  northwest-south- 
east trend,  the  pah  a  of  McGee,  are  particularly  notable.  The 
writers  have  little  data  in  hand  showing  definitely  the  presence 
of  lowan  drift  in  this  area  even  as  far  east  as  the  Wapsipinicon 
valley  in  western  Clinton  county.  There  is  even  more  question 
as  to  the  extension  of  the  lowan  ice  farther  east.  The  inherent 
improbability  of  the  extension  of  such  a  lobe  increases  with  the 
distance.  This  part  of  the  Wapsipinicon  valley  is  evidently  one 
of  the  oldest  valleys  in  eastern  Iowa.  It  is  pre-Kansan  if  not 
preglacial  in  origin.  The  relatively  low  elevation  of  the  land  for 
a  distance  of  six  to  eight  miles  north  of  the  stream  is  probably 
due  to  early  denudation.  Tributary  valleys  filled  by  Kansan 
drift  have  not  been  reexcavated  so  that  though  there  is  little 
irregularity  of  the  surface  the  thickness  of  the  drift  ranges  from 
a  foot  or  less,  at  points  where  the  limestone  is  exposed,  to  220 
feet  or  more  as  shown  by  wells.  Much  of  this  area  lies  below  the 
level  of  submergence  caused  by  the  shifting  of  Mississippi  river 
through  the  Goose  Lake  channel  at  the  time  of  the  Illinoian  ice 
invasion  (that  is,  700  to  720  feet  above  the  sea  level).  From 
this  submergence  may  have  resulted  the  deposition  of  much  of 
the  sand  found  throughout  this  area  and  as  a  consequence  some 
of  the  smoothing  of  the  contours.  Sand  deposited  on  the  lower 
levels  has  also  been  blown  about  and  has  mantled  some  of  the 
higher  tracts.  The  relatively  low  relief,  together  with  the  rela- 
tively short  time  since  the  disappearance  of  the  Illinoian  ice  and 


IOW AN  DRIFT  IN  CEDAR  COUNTY  179 

the  drainage  of  the  submerged  areas,  has  not  favored  subsequent 
dissection.  These  conditions  may  also  account  for  the  very 
moderate  amount  of  modification  of  the  till  noted  at  several 
places  where  test  borings  were  made  in  the  region  east  of  De- 
Witt.  There  is,  therefore,  considerable  ground  for  question  as 
to  the  lowan  ice  really  having  invaded  Clinton  county  to  any 
great  extent,  even  if  it  reached  as  far  east  as  Wheatland.  It 
may  be  possible  that  the  lowan  ice  front  curved  in  southwestern 
Jones  county  in  the  region  of  Morley  and  swung  southwestward 
to  Cedar  river  as  far  we&t  as  Lisbon  in  southeastern  Linn  county, 
so  that  there  may  have  been  no  Clinton  lobe  of  the  lowan  sheet. 
This  must,  however,  still  be  regarded  as  an  open  question. 

The  tract  west  of  Tipton  in  Cedar  county  which  shows  some 
lowan  characteristics  is  small  and  so  isolated  in  the  midst  of  a 
region  of  erosional  topography  that  the  writers  are  loth  to  think 
that  a  lobe  of  the  lowan  ice  lay  over  it.  It  differs  but  little  from 
an  area  of  little  dissected  Kansan  upland  in  the  southeast  part 
of  the  county  in  the  vicinity  of  Sunbury,  yet  the  relations  of  the 
loess  and  of  several  paha  render  it  like  some  lowan  tracts. 
Most  of  the  cuts  seen  between  Cedar  Bluff  and  Tipton  show 
only  loess  or  dune  sand.  A  cut  and  boring  on  the  nearly  flat  up- 
land north  of  Buchanan  showed  the  presence  of  what  appeared 
to  be  the  super-Kansan  "gumbo"  at  the  top  of  leached  and 
oxidized  till.  One  boring  on  this  upland  showed  calcareous  till 
immediately  below  thin  loess.  Considering  everything,  and 
especially  the  erosional  character  of  the  topography  surrounding 
this  small  area  it  seems  doubtful  if  the  lowan  ice  ever  occupied 
the  tract  in  question. 

Concerning  that  part  of  the  tract  north  of  Cedar  Bluff  (and 
the  same  is  true  of  the  whole  belt  northwest  to  the  vicinity  of 
Mount  Vernon),  Professor  Norton  wrote:64 

*  *  *  In  this  limited  area  the  aspect  of  the  topography  is 
abnormal  in  the  depth  of  the  rock-cut  valleys,  the  width  of  flood 
plains,  and  the  amount  of  dissection.  The  bowlders  scattered 
over  the  surface  and  the  fact  that  it  lies  in  the  direct  and  only 
path  to  the  typical  lowan  area  west  of  Tipton,  are,  perhaps, 
sufficient  reasons  for  mapping  this  region  of  western  Linn 
township  as  lowan,  although  the  ice  here  passed  over  without 

"Iowa    Geol.    Survey,    Vol.    XI,    p.    372 


180  THE   IOWAN  DRIFT 

altering  to  any  marked  degree  the  lie  of  the  land.  Here  no  clear 
marginal  ridge  marks  the  separation  from  the  Kansan  to  the 
north  and  it  is  hard  to  draw  the  line  of  demarkation  except  by 
the  border  line  of  the  loess  and  the  height  of  adjoining  lowan 
areas. 

It  may  be  that  the  limit  of  the  lowan  ice  advance  extended 
southwest  from  the  region  of  Libson  to  and  across  the  Cedar 
valley.  The  relations  of  the  loess,  the  presence  of  paha  and 
bowlder's  and  a  rather  smooth  topography  led  to  the  mapping 
of  lowan  drift  southeastward  to  and  beyond  Solon.  The  writers 
have  no  definite  evidence  of  the  presence  of  lowan  drift  in  this 
area.  Kansan  drift  with  super-Kansan  "gumbo"  was  observed 
in  the  dissected  belt  bordering  Cedar  river,  three  miles  north- 
east of  Solon  as  described  on  page  195,  but  with  no  overlying  till. 

If  the  lowan  ice  really  occupied  the  plains  on  both  sides  of  the 
river  as  far  southeast  as  Lisbon  and  Solon,  it  seems  necessary 
to  suppose  that  it  occupied  the  valley  as  well.  Subsequent  ero- 
sion, mantling  by  the  loess  and  the  gullying  of  the  same,  have 
removed  or  obscured  whatever  trace  of  the  presence  of  the  ice 
was  left.  The  same  is  true  of  the  slopes  bordering  Iowa  river 
southwest  of  Solon. 

Conditions  on  and  about  North  Liberty  plain  have  been  care- 
fully studied  by  Mr.  Leighton.65  Perhaps  the  most  important 
evidence  of  the  presence  of  the  lowan  till  is  found  in  the  electric 
railway  cut  north  of  Iowa  river,  described  on  page  117  (Plate  VII 
and  figure  10).  Here  there  is  a  bed  of  till,  presumably  post- 
Kansan,  overlying  a  crumpled  bed  of  deeply  weathered  gravel. 
Beneath  this  is  till  regarded  as  Kansan.  Nowhere  west  of  John- 
son county  does  the  lowan  ice  appear  to  have  crossed  or  even 
extended  to  the  valley  of  Iowa  river,  unless  it  be  in  the  vicinity 
of  Albion  in  Marshall  county.  The  upland  tract  in  southwestern 
Tama  county,  mapped  by  Professor  Savage  as  lowan,  seems  to 
the  writers  clearly  Kansan. 

No  marginal  moraine  phenomena  were  noted  along  the  south- 
ern border  of  the  lowan  area.  The  absence  of  such  phenomena 
and  the  erosional  character  of  the  topography  for  some  distance 

«6Leig-hton,  M.  M.,  The  Pleistocene  history  of  the  Iowa  River  Valley,  north  and 
west  of  Iowa  City  in  Johnson  County,  Iowa,  Iowa  Geological  Survey.  Vol.  XXV. 
(1914),  pp.  103-181,  1916. 


LITHOLOGIC  COMPOSITION  OP  DRIFT  181 

north  of  Iowa  river  permit  considerable  difference  of  opinion 
as  to  the  limits  of  the  lowan  ice  sheet. 

As  noted  above,  the  writers  did  not  make  a  careful  and  detailed 
study  of  the  marginal  parts  of  the  lowan  drift  such  as  would 
be  necessary  to  determine  accurately  its  limits  in  all  places. 
However,  while  there  is  so  much  uncertainty  about  the  exact 
limits  of  the  lowan  drift  south  and  west  of  northern  Delaware 
county,  one  should  not  lose  sight  of  the  large  amount  of  evidence 
of  the  presence  of  a  post-Kansan  drift  in  the  area  as  a  whole 
north  and  west  of  these  uncertain  limits. 


APPENDIX  A 

Tables  Showing  Lithologic  Composition  of  Drift. 

In  making  analyses  one  hundred  to  seven  hundred  pebbles 
were  collected  from  the  drift  at  each  of  the  places  indicated. 
These  were  sorted  and  the  percentages  taken.  These  include  nu- 
merous estimates  made  in  1907  by  R.  T.  Chamberlin.  Excepting 
the  analyses  by  Mr.  Chamberlin,  careful  determination  of  the  dif- 
ferent varieties  of  crystalline  rock  was  not  attempted,  only  the 
main  groups  being  differentiated.  The  averages  of  the  several 
types  of  crystalline  rock  are  therefore  only  approximately  cor- 
rect. The  totals  of  the  several  averages  of  the  crystallines  in 
each  table  would  approximate  the  percentage  of  foreign  material 
in  the  drift  since  no  igneous  crystalline  rock  formations  occur  in 
Iowa.  Those  nearest  to  the  north  are  in  Minnesota  and  Canada. 
The  quartzites  are  probably  principally  from  the  Huronian 
quartzite  areas  of  northwestern  Iowa,  eastern  South  Dakota,  and 
southern  Minnesota. 

In  collecting  pebbles  calcareous  concretions  and  clay  iron- 
stones were  generally  avoided.  These  are  not  regarded  as  ori- 
ginal constituents  but  as  having  formed  in  the  drift  since  it  was 
deposited.  In  making  up  the  averages  fractions  have  generally 
been  discarded. 


182 


THE   IOWAX   DRIFT 


fe;  15 


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NOinog;  Jo  xsaAi 


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'DO    Nn>IKVH>] 


'oo  oaaoo  oaaao 


1—  1  i—  1  r-l  CO  JO  T-t  T-l  1—  1  r~  1—  1 


i—  1  iH  CQ  OO  iH  i—  1 


^     -•  s 


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'oo  oaaoo  oaaao 

r-t           CM                                                                    CM 

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PEBBLES  F 

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ROM  IOWAN 

£   s^   ^ 

DRIFT 

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NOXNIA  -iO   HXHO>J 

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183 


384 


THE   IOWAX   DRIFT 


TABLE  III. 


ESTIMATE  OF  PEBBLES    FROM    LEACHED    PART  OF  UPPERMOST    TILL 
OF  IOWAN  DRIFT  AREA. 

BY  R.  T.  CHAMBERLIN,  1907,  AND  W.  C.  ALDEN  & 
M.  M.  LEIGHTON,  1914. 


CHICKASAW  Co. 
SIO.  OF  NEW  HAMPTON 
CHAMBERLIN 

FAYETTE  Co. 
OELWEIN  CUT 
CHAMBERLIN 

BUCHANAN  Co. 
Do:  is  GRAVEL  PIT 
CHAMBERLIN 

f^JSNTON  CO. 

NW.  OF  URBANA 

ALDEN 

£ 

K 

O 
ffi 

c< 

f-l 

!  -'.^N'l'ON  CO. 

W.  OF  KEYSTONE 
ALDEN 

LINN  Co. 
?EC.  29,  OTTRU  CREEK  TP. 

A  I.I.'KN 

H 
0 

< 

Greenstone  

24   . 

32 

34 

GO 

42 

40 

41 

39 

Greenstone  schist  

2 

4 

1 

Granite  and  gneiss 

24 

10 

12 

24 

22 

28 

10 

18 

Gabbro  diorite    _           —    — 

10 

2 

4 

?, 

Syenite 

2 

Porphyry  

8 

1 

Other  crystallines  ___ 

6 

2 

6 

2 

Qnartzite 

2 

6 

5 

4 

2 

5 

4 

Quartzose 

2 

2 

4 

1 

Quartz  

12 

10 

20 

6 

7 

Sandstone 

10 

4 

4 

2 

10 

4 

Dolomite  and  limestone  
Chert 

8 
4 

10 
10 

16 

30 

22 

5 

29 

3 
16 

Shale 

2 

Clav  ironstone 

4 

1 

Hematite  and  jasper 

Unidentified      

PEBBLES  PROM  BUCHANAN  GRAVEL 


185 


TABLE  IV. 

ESTIMATE  OF  PEBBLES  FROM  BUCHANAN  (?)   GRAVEL  IN  IOWAN 

DRIFT  AREA. 
BY  R.  T.  CHAMBERLIN,  1907,  AND  W.  C.  ALDEN  &  M.  M.  LEIGHTON,  1914. 


-£4 

•< 

b 

^ 

h 

S. 

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5 
o'z 

£ 

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gffi 

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0  3 

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3 

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HOWARD 

SW.  OF 

CHAMB 

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ggg 

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JHICKAS 
WEST  c 
CHAMB 

BREMER 
CREEK 
ALDEN 

FAYETTE 
OELWEI 
CHAMB 

BENTON 
NEAR  I 
ALDEN 

i 

8«| 

523 
§*< 

AVERAGE 

Greenstone 

25 

14 

24 

26 

35 

12 

38 

28 

39 

27 

Greenstone 

schist 

-1 

Granite  and 

gneiss 

20 

24 

17 

34 

27 

20 

24 

32 

23 

26 

Gabbro-diorite  — 

5 

8 

7 

6 

3 

Syenite          

4 

1 

1 

Porphyry    _    

1 

2 

1 

2 

2 

1 

Other 

crystallines  ___ 

6 

10 

4 

8 

3 

Quartzite 

7 

4 

2 

2 

12 

14 

8 

5 

6 

Ouartzose   - 

Quartz 

,, 

18 

16 

10 

8 

2 

6 

7 

Sandston° 

2 

1 

4 

2 

4 

1 

2 

Dolomite   and 

limestone  
Chert  

3 

8 

12 
2 

54 

14 

7 

8 

14 

22 

26 

12 
11 

11 
11 

Shale            

2 

4 

1 

Clay  ironstone— 

1 

2 

12 

2 

P"rnf»tite  and 

Jasper 

Fnidentified  - 

2 

6 

3 

1 

186 


THE  IOWAN   DRIFT 


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H3AIH  VMOI  HV3N 
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CO                                                       TH         CO 

xacriv 
xno  NiaAnao 

*    9              •"       «• 

CO 

xaa'iy 
3N33;H  ^o  xsvg 

T-l         CM                                                       S 

-amg  'xno  xi3A\Tao 

a«s«           «»B  «  c. 

NrraaawvHO  '>iovaa 
-amg  'xno  xiaAnao 

00        Ol-r-i              CO              COIOr-HlOCOC^        T—  1 

1—  1                                                  10 

NnaaawvHO  'aanovaq 

'GO    aXXSAV^ 

O         ^O  ^                      <N         (M         OO 
CO         CO                                                        i—  1 

CM 

xno  xiiAvaao 

O  ^-S  ^1                                       C^  C^l  OO  ^ 

xosmv  ^o  xsva 
•oo  Jia^ng 

C-5       o>             T?       cp       O       ^f  ^                  ^f 

ixio   saaavHO 
•oo  aAOij3 

£  %         ~  -*  ^ 

VXSIA  vx-iv  ava.M 

•OO    AVVSVHDIHC 

t^iMt^oo      r-ics           caor^io               «o 

XOXdKVH  A13X  ^0  '3S* 
'OO    AiVSV>IDIHO 

gJCO,H^^        00*        WC^^rH 

rH        CO 

NnnaawvHO 
soxiaas  SKI-J 
•oo  aavAiOH 

(7^  ^  O  "3«              (N  C<I        «O  C<I  CM  ^  00               •"*! 

TH           1-1                                                                         Tl< 

0 

1 

«1           8              1 

.22  §              c                 S 
^TS^        5                9 

««G_0             M        0        Ora 

^"g^  2^^^'B-M^"*'sJ 
5  O  5  O  &  iS  6  C'C'Sc^  C  C  o 

Clay  ironstone  -  
Hematite  and  jasper.  _  
Unidentified  . 

PEBBLES  FROM  KANSAN  TILL 


187 


TABLE  VI. 

ESTIMATES  OF  PEBBLES  FROM  THE  LEACHED  AND  OXIDIZED  UPPER 
PART  OF  THE  KANSAN  TILL  OUTSIDE  OF  IOWAN  DRIFT  AREA. 

BY  R.  T.  CHAMBERL1N,  1907,  AND  tW.  C.  ALDEN  &  M.  M.  LEIGHTON,  1914-15. 


2 

ft 

g      - 

.98 

n"3 

*ls 

3  2 

&A 

NI11 
•nVHSH1 

•00  ' 

8 

z 

^L 

0 

1 

WAHREN  < 

CltURCHi 

CHAMBEI 

WARREN  < 
CHURCIH 
CHAMBEI 

WARREN  ( 

CHURCH! 

CHAMBEI 

WAPELLO 
RIVERVIE 
CHAMBEI 

VIARSHALI 
S.  OF  Mf. 

CHAMBEI 

MARSHALI 

SE.  PAR' 

ALDEN 

TAMA  Co. 
WEST  OF 

AI.DKX 

vVlNNESH 

EAST  OF 
CHAMBEI 

UNION  Co 
AFTON  J 
LEIGHTO: 

AVERAGE 

Greenstone 

10 

6 

10 

16 

30 

34 

22 

16 

27 

19 

Greenstone 

schist 

2 

2 

2 

4 

2 

1 

Granite  _    _  -  

15 

10 

14 

12 

12 

30 

16 

26 

15 

17 

Gabbro-diorite  — 

1 

4 

4 

16 

8 

14 

5 

Syenite 

2 

2 

2 

8 

2 

Porphyry 

4 

1 

Other 

crystallines  ___ 

9 

6 

2 

2 

6 

9 

4 

Quartzite 

14 

40 

32 

10 

4 

6 

6 

6 

20 

15 

Quartzose 

/> 

2 

2 

4 

2 

2 

Quartz 

8 

14 

10 

4 

6 

14 

5 

7 

Sandstone      -  

4 

2 

2 

16 

6 

3 

Dolomite   and 

3 

2 

12 

6 

3 

limestone  

Chert             _      _ 

20 

12 

20 

8 

22 

12 

42 

4 

16 

Shale 

2 

2 

2 

4 

4 

8 

2 

Hematite  and 

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THE   IOWAX   DRIFT 


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190  THE   IOWAN   DRIFT 

APPENDIX  B 

Notes  on  Exposures  of  Super-Kansan  "Gumbo"  in  the  Kansan 
Drift  Area. 

Among  the  most  interesting  exposures  of  what  is  regarded 
as  super-Kansan  " gumbo"  were  those  afforded  by  the  new  cuts 
on  the  Chicago,  Milwaukee  &  St.  Paul  railway  in  adjacent  parts 
of  Story  and  Marshall  counties  where  the  railroad  runs  eastward 
from  the  "Wisconsin  drift  area  of  the  Des  Moines  lobe  into  the 
Kansan  drift  area.  The  railway  runs  down  a  creek  valley  and 
cuts  the  spurs  of  the  slopes  from  which  in  places  the  Wisconsin 
drift  is  absent,  as  it  has  been  cut  away  by  erosion.  Going  east 
from  the  first  road  crossing  west  of  the  Marshall-Story  county 
line  the  following  was  noted. 

STORY  COUNTY. 

COLLINS  TOWNSHIP,  TOWNSHIP  82  NORTH,  RANGE  21  WEST,  SECTION  13, 
SOUTHWEST  QUARTER. 

1st,  2d  and  3d  cuts  east  of  crossing  are  all  in  Wisconsin  till,  calcareous  nearly 
or  quite  to  top. 

3d  cut  is  30±  feet  deep  and  the  core  of  the  spur  is  gray  till  while  over  that 
the  till  has  grayish  buff  tint.  This  is  at  the  block-signal. 

4th  cut  is  for  the  most  part  all  in  loess.  In  the  eastern  part  Wisconsin  gray 
till  is  banked  against  and  over  10  +  feet  of  loess. 

5th  cut,  gray  noncalcareous  "gumbo," — face  of  cut  sun-checked. 
6th  cut,  gray  clay,  "gumbo" (?)    containing  lime  concretions  but  itself  non- 
calcareous,  sun-checked,  overlying  buff-yellow-brown  oxidized  and  leached  Kan- 
san till. 

7th  cut  for  ditch  on  curve,  yellow,  oxidized  Kansan  till,  15  feet. 

FEET 

8th  cut,  Buff-brown  loess 5-6 

Gray  loess   4 

Dense  gray  "gumbo,"  sun-checked 15 

Rusty  till,  Kansan,  slightly  exposed. 

9th  cut  for  ditch  at  electric  signal  at  county  line: 

FEET 

Gray  loess  4-5 

Yellow,  oxidized  till,  Kansan 10 

MARSHALL  COUNTY. 
EDEN  TOWNSHIP,   SECTION  19    (TOAVNSHIP  82   NORTH,  RANGE  20  WEST). 

10th   (big  cut):  FEET 

Buff,  calcareous  till,  Wisconsin  8 

Gray  loess,  contorted  streaks  at  top,  f ossilif erous ? 

Dense,  pebbleless,  gray,  noncalcareous  "gumbo,"  sun-checked..         ? 

Yellow,  oxidized  till,  Kansan ? 

Down  to  track  and  below  the  track  in  ditch  as  at  9th  cut. 


"GUMBO"  IN  MARSHALL  COUNTY  191 

llth,  big  cut  across  curve  of  old  line,  60  feet  (per  barometer)  deep  at  maxi- 
mum (see  Plate  XIII): 

FEET 

Loose,  buff  till,  Wisconsin,  leached  5-6  feet,  calcareous  below..      25 
Buff  loess,  full  of  lime  concretions  in  lower  part.     Irregular 
ferruginous  line  or  shell  2-3  inches  thick,  partly  cut  off  at  base 

of  Wisconsin  0-15 

Grayish,  calcareous  loess 0-15 

Noncalcareous  gray  "gumbo,"  containing  a  few  small  pebbles', 

sun-checked    7.3 

Yellow,  oxidized  till,  Kansan 5-8 

More  of  the  Kansan  till  is  exposed  to  the  east  as  the  track 
lowers.  Where  twelve  feet  is  exposed  a  finely  glaciated  lime- 
stone bowlder  three  by  five  feet  in  size  lies  in  the  lower  part. 
Farther  east  an  equally  large  and  finely  glaciated  granite  bowl- 
der lies  near  the  top  of  the  Kansan  in  the  lower  part  or  at  the 
bottom  of  the  gray  "gumbo,"  which  is  here  about  ten  feet  thick. 
Near  the  east  end  of  the  cut  is  a  block  of  gray,  ripple-marked 
sandstone  (calcareous).  The  loess  runs  down  the  slope  to  the 
east  at  least  as  low  as  the  track,  over  the  * '  gumbo ' '  and  Kansan 
till.  The  Wisconsin  is  present  only  at  the  top  of  the  deepest 
part  of  the  big  cut  (No.  11). 

East  of  Rhodes,  Eden  township,  section  10,  northwest  quarter, 
and  between  two  and  three  miles  east  of  the  limit  of  the  Wiscon- 
sin drift,  the  following  was  seen  near  "Station  1  mile"  post 
(figure  34). 


Figure  14 — Diagram  of  drift  pypo?ed  on  Chif>p<ro,  Milwaukee  and  St.  Paul  Rail- 
way cut  east  of  Rhodes,  Iowa.  Aftonian  (t)  sand  and  gravel  (1), 
Kansan  till  (2),  super-Kansan  "gumbo"  (3),  loess  (4). 

DRIFT  EAST  OF  RHODES,   IOWA. 

FEET 
At  west  end  of  cut: 

4.     Loess,  buff  to  grayish,  leached  6-8  feet,  calcareous  in  lower 

part  with  calcium  carbonate  concretions   10 

3.     "Gumbo,"  dense,  sticky,  gray,  noncalcareous  clay  contain- 
ing some  small   pebbles    (cut  away  to   east   by   pre-loess 

erosion )    10 

2.     Till   (Kansan),  loose,  rather  sandy,  rusty  yellow. 
Farther  east  in  the  cut  and  below  the  loess: 

2.     Till    (Kansan),    dark   reddish   to   purplish    brown    at   top, 

brown  to  grayish  below,  leached 6-8 

1.     Sand  and  gravel   (Aftonian?),  rusty,  buff  to  brown,  loose, 

stratified,  in  places  cemented  by  iron  oxide;  exposed 5-8 

This  sand  and  gravel  extends  farther  east  below'  the  track  level. 


192  THE   IOWAX   DRIFT 

A  cut  one-half  mile  east  of  Melbourne  exposes  about  ten  feet 
of  iioncalcareous,  gray  " gumbo"  beneath  ten  feet  of  loess. 

One  mile  east  of  Haverhill  (southwest  quarter  of  section  3, 
Jefferson  township,  township  82  north,  range  18  west)  a  cut  on 
the  Chicago,  Milwaukee  and  St.  Paul  railway  exposes: 

DRIFT  EAST  OF  HAVERHILL,  IOWA. 

FEET 

4.     Loess,  buff,  leached  9-10 

3.     Loess,  buff  to  gray,  calcareous 5 

2.     "Gumbo,"  dense  gray  clay,  noncalcareous  and  containing  a 

few  small  cherts  4-8 

1.     Till,  Kansan,  exposed  at  one  point. 

Between  two  and  three  miles  south  of  this  place  (section  22. 
west  line  of  northwest  quarter)  the  " gumbo"  is  exposed  in  the 
road  ditch  below  three  feet  of  loess  on  the  slope  north  of  the 
cemetery.  Here,  there  appears  to  be  a  gradation  from  the 
"gumbo,"  which  is  gray  and  mottled  rusty  brown  in  the  lower 
part,  downward  into  the  leached,  rusty,  grayish  brown  till  below. 
In  the  gumbo  are  small  pebbles,  mostly  cherts  with  some  frag- 
ments of  granite,  feldspar,  etc.  In  the  gradation  zone  is  a 
granite  bowlder  one  foot  by  one  and  one-half  feet  in  diameter 
which  is  crumbling  to  pieces  and  in  which  the  feldspars  are 
decomposing.  The  relations  strongly  suggest  that  the  "gumbo" 
may  be  the  product  of  long  weathering,  thorough  leaching,  and, 
finally,  deoxidation  of  the  till. 

"Gumbo"  was  seen  also  in  a  road  cut  one  and  one-half  miles 
north  of  Haverhill  and  in  a  railroad  cut  east  of  Pickering. 

POWESHIEK  COUNTY. 

An  exposure  in  a  road  cut  several  miles  southeast  of  Grinnell, 
Poweshiek  county  (Pleasant  township,  Township  79  North, 
Range  15  West,  section  5,  south  line),  showed  five  or  six  feet 
of  dense  tough  "gumbo"  near  the  top  of  a  slope  and  thirty  feet 
above  the  neighboring  valley.  The  "gumbo"  here  is  brown  at 
the  top  with  scattered  red  spots,  and  grayish  brown  below.  It 
has  a  small-lump  or  "buckshot"  texture.  Similar  ' ' gumbo ' '  was 
observed  in  a  road  cut  at  a  point  northeast  of  Grinnell  (in  Mal- 
colm township,  section  6,  south  line  of  southwest  quarter).  The 
"gumbo"  here  outcrops  in  a  slope  about  fifteen  feet  from  the 
top  of  the  hill,  which  is  a  little  lower  than  the  upland  level. 


GUMBO  IN  IOWA  COUNTY  193 

Another  exposure  of  the  "gumbo"  was  seen  about  sixteen 
miles  farther  east  in  a  road  cut  on  the  west  line  of  the  southwest 
quarter  of  section  1,  Warren  township,'  (Township  80  North, 
Range  13  West)  and  two  miles  north  of  the  railroad,  near  Victor. 
The  succession  in  the  slope  just  north  of  the  southwest  corner 
was  as  follows: 

DRIFT  NEAR  VICTOR. 

FEET 

4.     Loess    4 

3.     "Gumbo,"  dense,  noncalcareous  clay,  gray  with  red  spots ...          % 

2.  Till   (Kansan),  brown,  leached 7 

1.  Till  (Kansan) ,  calcareous;  exposed 3 

An  estimate  of  pebbles  from  No.  1  is  given  in  Table  7,  Appen- 
dix A.  It  will  be  noted  that  it  does  not  differ  materially  from 
the  other  estimates  of  either  the  Kansan  or  pre-Kansan  drift. 

IOWA  COUNTY. 

"Gumbo"  was  observed  in  the  southeastern  part  of  Iowa 
county  six  miles  east  of  Parnell,  near  the  bottom  of  the  side 
slope  of  a  small  valley  which  cuts  the  north  slope  of  the  ridge 
between  Old  Man  and  Deer  creeks  (just  west  of  the  corner  near 
the  middle  east  line  of  section  3,  Greene  township,  Township  78 
North,  Range  9  West).  The  beds  exposed  were  as  follows: 

DRIFT  EAST  OF  PARXELL,  IOWA. 

FEET 

3.  Loess    ' 3-5 

2.  "Gumbo,"  dense,  brown  .at  top,  gray  below,  noncalcareous, 
contains  a  few  small  pebbles 3 

1.    Till  (Kansan),  reddish  brown,  leached. 

No  boring  was  made  to  determine  whether  or  not  the  gumbo 
extends  back  into  the  hill  between  the  loess  and  the  till.  The 
"gumbo"  here  is  sixty  feet  or  so  below  the  level  of  the  highly 
oxidized  top  of  the  till  exposed  on  top  of  the  ridge  one  mile  west, 
and  is  somewhat  lower  than  the  weathered  top  of  the  till  exposed 
in  the  north-south  road  farther  south. 

Four  miles  south  (west  line  northwest  quarter  section  27)  a 
road  cut  along  the  side  slope  about  twenty  feet  below  the  top  of 
the  ridge  exposed: 

13 


194  THE   IOWAN   DRIFT 

DRIFT  SOUTHEAST  OF  PABXELL,   IOWA. 

FEET 
3.     Loess,  buff    

2.  "Gumbo,"  noncalcareous  clay,  upper  1-1%  feet  brown  with 

red  spots,  gray  below 5-6 

1.  Till    (Kansan),  brownish   yellow,   leached. 

Two  miles  northwest  of  this  place  (middle  east  line  section 
19)  " gumbo"  is  exposed  at  about  the  same  elevation  but  the  cut 
is  near  the  foot  of  the  slope  east  of  the  creek  and  is  sixty  feet 
lower  than  the  top  of  the  ridge  less  than  one-half  mile  north. 
The  beds  here  are  as  follows : 

DRIFT  SOUTHEAST  OF  PARXELL,  IOWA. 

FEET 

3.  Loess    . 

2.  "Gumbo,"  dense,  gray  clay,  noncalcareous,  contains  small 

chert  and  quartz  pebbles  few  feet 

1.  Till  (Kansan),  oxidized,  red. 

Two  miles  southeast  of  Parnell  (Fillmore  township,  Township 
78  North,  Range  10  West,  section  12,  west  line)  a  road  cut  across 
a  spur  near  the  upland  level  exposed: 

DRIFT  SOUTHEAST  OF  PARXELL,  IOWA. 

FEET 

3.  Loess,  buff 3 

2.  "Gumbo,"  upper  1-1%  feet  reddish,  gray  below 4-5 

1.     Till   (Kansan),  oxidized  and  leached. 

It  thus  appears  that  not  all  the  occurrences  of  " gumbo"  are 
at  the  upland  level  and  in  places  neighboring  exposures  at  higher 
levels  show  only  the  red  or  brown  oxidized  till  beneath  the  loess. 
Possibly  some  of  the  occurrences  at  relatively  low  levels  are  due 
to  redeposition  afterward  from  the  uplands,  or  they  may  be 
outcrops  of  pre-Kansan  "gumbo". 

WASHINGTON  COUNTY. 

About  eight  miles  west  of  Washington,  Dutch  Creek  township 
(Township  75  North,  Range  8  West,  section  24,  south  line),  gray 
" gumbo,"  sticky,  gritty,  and  noncalcareous,  was  observed  out- 
cropping on  a  slope  beneath  the  brown  loess.  This  clay  is  pebbly  a 
short  distance  below  the  top  and  contains  some  concretions  of 
calcium  carbonate  or  else  it  grades  into  till  of  the  same  color  and 
texture.  A  slight  exposure  of  the  " gumbo"  was  seen  about  one 
mile  west  of  Washington  and  another  about  nine  miles  southeast 
of  the  same  place. 


GUMBO  IN  CEDAR  COUNTY  193 

JOHNSON  COUNTY. 

About  three  miles  northeast  of  Solon  (Cedar  township,  Town- 
ship 81  North,  Range  5  West,  section  7,  east  line  northeast 
quarter),  the  following  was  seen: 

DRIFT  NORTHEAST  OF  SOLON. 

3.     Loess,  buff   FE^J 

2.     "Gumbo,"  dense  sticky,  dark  gray  clay,  noncalcareous  and 

containing  scattered  small  chert  and  quartz  pebbles  5 

1.  Till    (Kansan),  rusty  brown,  leached. 

About  one-fourth  mile  northwest,  around  the  corner  (on  the 
north  line  of  the  northeast  quarter  of  section  7)  the  road  cut 
exposes  only  loess,  but  a  boring  in  the  bottom,  together  with  the 
cut,  showed  the  same  succession  of  deposits  as  that  noted  above. 

A  well  on  top  of  the  ridge  to  the  south  was  said  by  the  owner 
to  penetrate  228  feet  of  drift,  mostly  clay  with  sand  at  the  bot- 
tom. Some  wood  was  encountered  about  200  feet  from  the  sur- 
face, or  about  150  feet  lower  than  the  " gumbo."  W.  Verba's 
well  in  section  6  is  reported66  as  being  drilled  through  the  fol- 
lowing deposits : 

LOG  OF  W.  VERBA'S  WFXL. 

FEET 

4.     Reddish  clay  (loess  or  Kansan?) 20 

3.     Blue  clay,  yellow,  sandy  (Kansan?) 100 

2.  Black  soil  (Aftonian?)   2 

1.     Brownish  clay  and  yellow  clay  (pre-Kansan)  above  rock..      10 

CEDAR  COUNTY. 

About  six  miles  west  of  Tipton  (Cedar  county,  Cass  township, 
TownsEip  81  North,  Eange  3  West,  section  31,  south  line  of 
southwest  quarter)  a  shallow  road  cut  on  the  nearly  flat  upland 
exposes  rusty,  ashen-gray,  pebbly  clay  with  the  texture  and  ap- 
pearance of  "gumbo."  In  a  boring  here  the  auger  penetrated 
the  following: 

DRIFT  WEST  OF  TIPTON,  IOWA. 

FEET 

Brownish  gray  pebbly  clay,  "gumbo"? 4 

Till   (Kansan?),  brown,  leached 3 

Till   (Kansan?),  brown,  calcareous. 

It  is  suggested  that  this  gently  undulating  plain,  some  fifteen 
square  miles  in  extent,  which  has  been  mapped  as  lowan,  may  be 
a  remnant  of  the  Kansan  upland  whose  dissection  has  been  re- 
tarded by  the  gorge  cutting  of  Cedar  river  between  Cedar  Bluff 

MU.  S.  Geol.  Survey  Water  Supply  Paper  293,  p.  425, 


196  THE   IOWAN   DRIFT 

and  Rochester  and  by  the  tributary  streams  having  to  work  so 
much  in  limestone.  Most  of  the  surrounding  area  and  especi- 
ally that  to  the  south,  is  much  dissected,  with  50  to  150  feet  of 
relief. 

About  four  miles  southwest  of  Lowden  (Springfield  township, 
Township  81  North,  Eange  1  West,  section  16  near  center)  a 
road  cut  on  the  lower  part  of  a  small  spur  showed,  below  three 
and  one-half  feet  of  loess,  two  and  one-half  feet  of  " gumbo," 
reddish  brown,  noncalcareous,  with  " buckshot"  texture  and  con- 
taining sand  grains  and  a  few  small  pebbles. 

A  small  exposure  of  "  gumbo  "-like  clay  was  seen  on  the  west 
side  of  Cedar  river,  two  miles  west  of  Moscow  (Muscatine 
county,  Moscow  township,  Township  77  North,  Eange  2  West, 
section  8,  southwest  quarter).  At  this  place,  below  five  to  fifteen 
feet  of  leached  buff  loess  is  dense,  gray,  noncalcareous  "gumbo- ' ' 
like  clay  two  to  two  and  one-half  feet  thick,  which  carries  as 
many  pebbles  as  the  till  below.  There  is  a  dark,  carbonaceous 
band  at  the  top  which  seems  to  be  due  to  vegetal  growth  in  an 
old  soil.  The  pebbly  " gumbo"  grades  below  into  brown  stony 
till.  This  exposure  is  but  twenty  to  forty  feet  above  the  bottom 
land  (at  660  to  680  feet  above  sea  level)  so  it  probably  does  not 
correspond  to  the  super-Kansan  upland  "gumbo." 

CLINTON  COUNTY. 

Going  northeast  across  the  gently  undulating  plain  of  the  so- 
called  Olinton  lobe  one  reaches  the  higher  hills  of  the  loess-Kan- 
san  tract  on  the  north.  Here  is  a  greatly  dissected  area  with 
100  to  150  feet  of  relief  and  with  steep  slopes  sharply  cut  by 
frequent  V-shaped  ravines.  At  many  of  the  places  where  the 
till  is  exposed  beneath  the  loess  its  upper  part  is  oxidized  to  a 
deep  red  f erretto.  In  a  few  cuts  there  was  seen,  in  place  of  this, 
a  well-marked  bed  of  "gumbo".  About  eight  miles  northeast 
of  DeWitt  (Washington  township,  Township  82  North,  Eange 
4  East,  section  22,  east  line  of  the  southeast  quarter,  at  760^ 
feet  above  sea  level)  a  cut  in  the  slope  fifty  to  sixty  feet  below 
the  upland  level  exposed  the  following : 


GUMBO  IN  JONES  COUNTY.  197 

DRIFT  NORTHEAST  OF  DEWrrr,  IOWA. 

FEET 

3.     Loess    6 

2.     "Gumbo" (?),  gray  clay,  a  few  inches,  and  a  pebble  band. . .          % 

1.     Till,  deep  red  ferretto,  exposed iy2 

Brown  till  leached. 

Three  miles  to  the  southeast  (Center  township,  Township  82 
North,  Range  5  East,  section  30,  east  line  of  the  northeast  quar- 
ter, at  77^  feet  above  sea  level)  the  "gumbo"  is  five  feet  thick. 
It  is  dense,  noncalcareous,  gray,  and  blackened  at  the  top  by  car- 
bonaceous matter  which  resembles  an  old  soil.  This  contains 
plentiful  small  pebbles,  most  of  which  are  chert  and  quartz  al- 
though some  are  crystallines.  Beneath  lies  the  till.  Near  the 
middle  of  the  south  half  of  the  same  section,  one-half  mile  dis- 
tant, what  appears  to  be  the  same  bed  of  "gumbo"  is  slightly 
exposed  below  a  grassed  bank  ten  feet  high  which  is  probably 
of  loess.  The  exposures  are  twenty  to  thirty  feet  below  the  top 
of  the  loess-mantled  ridge. 

In  the  much  dissected  elevated  tract  in  the  northwest  part  of 
Clinton  county,  at  one  point  (Sharon  township,  Township  83 
North,  Eange  1  East,  section  9,  middle  of  the  south  line)  there 
was  noted  beneath  the  loess  on  the  slope,  three  feet  of  dense, 
brown  to  gray  clay  containing  small  chert  and  quartz  pebbles  and 
much  like  the  "gumbo"  in  texture.  This  grades  downward  in- 
to stony  till.'  This  exposure  is  in  a  cut  on  the  steep  slope,  about 
sixty  feet  below  the  top  of  the  ridge.  Other  cuts,  some  nearer 
the  upland  level,  show  only  the  deep  red  ferretto  at  the  top  of 
the  till  and  beneath  the  loess. 

JONES  COUNTY. 

Several  miles  farther  west  another  deposit  which  suggested 
the  super-Kansan  "gumbo"  was  seen  at  a  point  two  to  three 
miles  north  of  Oxford  Junction  (Oxford  township,  Township  83 
North,  Eange  1  West,  section  10,  north  line  of  the  northeast 
quarter).  The  exposure  is  on  the  slope  of  a  lobe  of  the  ridge, 
about  thirty  feet  below  the  top.  Beneath  three  feet  of  brown 
loess  is  a  much  decayed  brown  gravelly  drift.  The  granite  and 
greenstone  pebbles  are  so  decomposed  as  to  be  readily  cut 
through.  Near  the  top  of  the  drift  are  streaks  and  patches  of 
grittv  gray  clay  which  suggests  "gumbo".  This  clay  increases 


198  THE   IOWAN   DRIFT 

in  amount  in  the  lower  part  of  the  exposure  as  though  it  were  due 
to  more  thorough  decomposition  below  the  gravelly  top.  In  the 
lower  part  of  the  seven  foot  bed  it  becomes  a  mixture  of  light 
gray  and  dark,  rusty,  brown  clay  full  of  arkosic  material.  This 
appears  not  to  be  a  deposit  distinct  from  the  underlying  till  but 
is  in  reality  the  much-weathered,  upper  part  of  the  till  so  far 
decomposed  and  with  so  much  of  the  soluble  material  removed 
that  it  approaches  in  character  the  super-Kansan  "gumbo"  seen 
elsewhere. 

Northwest  of  this  point  along  the  high-ridged  and  much  dis- 
sected belt  of  thick  drift,  numerous  cuts  expose  the  deeply  oxid- 
ized upper  part  of  the  till  beneath  the  loess  mantle,  but  no  other 
remnant  of  the  " gumbo"  is  known  east  of  the  Monticello-Ana- 
mosa  road  and  here  the  " gumbo"  is  overlain  by  lowan  till. 

SCOTT  COUNTY. 

Between  four  and  five  miles  west  of  LeClaire,  Scott  county 
(LeClaire  township,  near  middle  of  the  east  half  of  section  36, 
Township  79  North,  Eange  4  East),  an  interesting  exposure  was 
observed  in  September,  1915,  as  follows : 

DRIFT  NORTHEAST  OF  DAVENPORT,  IOWA. 

FEET 

4.     Loess,  buff   ) 

3.     Loess,  gray,  noncalcareous,  with  iron  oxide  pipes f  •1' 

2.  "Gumbo"  (super-Kansan),  dense,  gray,  noncalcareous  clay, 
showing  a  fine  network  of  rusty  seams  and  containing  a 

few  small  polished  quartz  pebbles  and  chert  fragments 4-5 

1.  Till  (Kansan?),  rusty  brown,  with  disintegrating  crystal- 
line pebbles  up  to  1  foot  in  diameter.  Lower  down  the 
color  becomes  lighter  brownish  yellow,  and  the  till  is 
calcareous  with,  in  one  place,  a  thin  crust  of  calcium  car- 
bonate several  feet  long. 

The  gray  ".gumbo"  (No.  2)  is  different  in  texture  from  the 
gray  loess  above,  being  more  dense  and  sticky  and  containing 
pebbles.  It  resembles  the  super-Kansan  "gumbo"  farther  west. 
The  till  resembles  the  Kansan,  and  the  Illinoian  till  is  apparently 
absent  at  this  point. 

ROCK  ISLAND  COUNTY,  ILLINOIS. 

The  upland  south  of  Mississippi  river  in  Rock  Island  county, 
Illinois,  is  considerably  dissected  by  erosion  and  much  of  the 
Illinoian  till  may  have  been  removed  before  the  loess,  which  is 


GUMBO  BENEATH  ILLINOIAN  TILL  199 

one  to  fifteen  feet  in  thickness,  was  deposited.  It  appears  to  be 
absent  at  the  following  places.  About  three  miles  southeast  of 
Illinois  City  in  Buffalo  township  (Township  16  North,  Range  4 
West),  just  east  of  the  middle  of  the  west  line  of  section  20, 
the  following  was  observed  in  a  road  cut,  in  September,  1915 : 

DRIFT  IN  ROCK  (ISLAND  COUNTY,  ILLINOIS. 

FEET 

3.     Loess,    brown,    leached 3± 

2.  "Gumbo,"    dense,    gray,    noncalcareous,    containing    small 
cherts  and  some  small  crystalline  pebbles 3± 

1.     Till,  brown,  leached. 

About  one  and  one-half  miles  farther  south  just  south  of  the 
middle  of  section  29,  the  following  was  seen : 

DRIFT  IN  ROCK  'ISLAND  COUNTY,  ILLINOIS. 

FEET 

3.  Clay  ("gumbo"?),  rusty  gray  3± 

2.     Till  (Kansan?) ,  brown,  leached  5± 

1.  Till    (Kansan?),  brownish  gray  with  abundant  limestone 
pebbles. 

GUMBO  BENEATH   ILLINOIAN   TILL,   LOUISA  COUNTY,   IOWA. 

In  this  connection  it  may  be  noted  that  the  Kansan  drift  and 
super-Kansan  "gumbo"  have  been  observed  beneath  the  Illi- 
nian  drift  in  both  southeastern  Iowa  and  western  Illinois. 

Certain  exposures  examined  on  the  upland  south  and  west  of 
Wapello  showed: 

DRIFT  IN  SOUTHWESTERN  LOUISA  COUNTY,  iIowA. 

FEET 

5.     Loess,  brown   8-10 

4.     Till    (Illinoian),  brown  and  leached  but  containing  lime- 
stone fragments    5-10 

3.     Clay    (silt  or   "gumbo,"   super-Kansan),   gray,   with   some 

small    pebbles    • 2-3± 

2.  Till  (Kansan),  brown,  leached,  rusty  red  on  joint  faces 6-7 

1.     Till    (Kansan) ,    brown,    calcareous 5± 

Limestone. 

HENRY  COUNTY,  ILLINOIS. 

A  " gumbo"  which  was  seen  at  one  exposure  in  Henry  county, 
Illinois,  is  quite  certainly  super-Kansan,  as  it  is  overlain  by  Illi- 
noian till.  The  exposure  is  on  a  spur  crossed  by  the  road  and 
east  of  the  creek  and  is  about  seven  miles  south  and  three  miles 
west  of  Cambridge,  in  Clover  township  (Township  14,  Range  2 
East,  section  14,  south  line  of  the  southwest  quarter).  It  shows 
the  following: 


200  THE   IOWAX   DRIFT 

DRIFT  SOUTHWEST  OF  CAMBRIDGE,  ILLINOIS. 

FEET 

4.  Clay,  brown,  loesslike  in  upper  part  but  with  small  pebbles 
lower  down.  These  increase  in  size  and  number  down- 
ward into  ( 3 )  few  feet 

3.     Till   (Illinoian),  brown,  leached  in  upper  part,  calcareous 

below,  with  calcium  carbonate  concretions  -. 10± 

2.  Clay  (super-Kansan  "gumbo"),  gray,  noncalcareous,  sticky, 
containing  small  cherts  and  some  lumps  of  rusty,  fer- 
ruginous clay  5 

1.  Till  (Kansan),  gray,  calcareous,  containing  rusty  iron 
oxide  masses  and  becoming  more  uniformly  brownish  lower 
down. 

This  occurrence  taken  with  those  cited  above  indicates  quite 
surely  that  there  is  a  super-Kansan  ''gumbo"  bed  underlying 
the  Illinoian  till.  This  is  clearly  distinct  from  any  super- 
Illinoian  "gumbo". 


APPENDIX  C. 

Occurrences  of  Drift,  Possibly  lowan. 

W'INNESHIEK  COUNTY. 

In  a  boring  at  a  point  three  miles  southwest  of  Ridgeway  (in 
Lincoln  township,  Township  89  North,  Range  10  West,  section  28, 
middle  of  west  line),  the  following  beds  were  penetrated: 

DRIFT  SOUTHWEST  OF  RIDGEWAY,  IOWA. 

FEET 

Loam,  sandy   1 

Till  (lowan?),  brownish  yellow,  leached. 2% 

Sand,  brownish  yellow,  leached 3% 

Silt,   loesslike,   gray,   leached 1 

CERRO  GORDO  COUNTY. 

The  only  exposure  seen  outside  the  Wisconsin  area  in  Cerro 
Gordo  county  which  suggested  the  presence  of  post-Kansan  till 
was  in  Portland  township,  section  17,  southeast  quarter.  A 
road  cut  in  the  abrupt  thirty-five  foot  slope  east  of  Lime  creek 
showed  the  following: 

DRIFT  BETWEEN  MA.SOX  CITY  AND  PORTLAND,  IOWA. 

FEET 
5.     Soil,  dark,  grading  into  loose,  buff,  leached,  pebbly  clay. ...        2 

4.    Clay,  dense,  gray,  pebbly,  lying  unevenly  on  Xo.  3 0-4 

3.     Sand,  in  irregular  streaks few  inches 

2.     Clay,    dense,    purplish,    leached,    "gumbo''-like,    uneven    as 

though  disturbed    0-1 

1.     Till,  highly  oxidized,  reddish,  gritty,  leached,  pebbly.     No 
limestone  pebbles  seen,  granites  disintegrating 5-8 


IOWAN    (?)    TILL  IN   BREMER  COUNTY  201 

Number  1  looks  like  the  Kansan  ferretto  of  southern  Iowa. 
Numbers  2  and  3  were  present  only  in  the  north  side  of  the  cut. 
The  upper  pebbly  clay,  Nos.  4  and  5,  might  represent  a  distinct 
till  sheet  later  than  No.  1,  though  this  clay  could  not  with  cer- 
tainty be  said  to  be  till. 

FLOYD  COUNTY. 

The  writers,  in  company  with  Prof.  A.  0.  Thomas,  examined 
the  following  section  exposed  at  an  old  quarry  in  the  southern 
part  of  Charles  City: 

DRIFT  AT  KUHXLE'S  QUARRY,  CHARLES  CITY,  IOWA. 

FEET 

5.  Loam,  sandy 1-2 

4.  Sand  and  gravel,  rusty,  containing  limestone  pebbles 6-8 

3.  Drift,  calcareous,  gray  to  yellow,  pebbly 0-1  % 

2.  Gravel,  rusty,  clayey,  containing  limesteone  pebbles 3-4 

1.  Till,  dense,  calcareous,  pebbly,  brown  at  top,  gray  below. .       4± 

Limestone  surfaces  show  striae  bearing  south-southeast.  Ac- 
cording to  Professor  Thomas,  Professor  Calvin,  who  examined 
this  exposure  with  him,  regarded  No.  1  as  Kansan  till,  No.  2 
as  Buchanan  gravel,  and  No.  3  as  lowan  drift.  To  the  present 
writers  it  seemed  very  uncertain  that  No.  3  was  a  distinct  de- 
posit of  glacial  till. 

CHICKASAW  COUNTY. 

A  road-cut  three  miles  south  of  Lawler  (Stapleton  township, 
Township  95  North,  Eange  11  West,  section  3,  west  line  of  the 
southwest  quarter)  exposed  rusty  brown  to  yellow  sand  and 
gravel,  poorly  assorted,  leached  throughout,  cemented  in  places 
at  the  bottom  by  iron  oxide.  At  one  end  buff  leached  till,  which 
ranges  from  nothing  to  six  feet  in  thickness,  overlies  the  rusty 
gravel  and  includes  a  bowlder  of  the  cemented  gravel  conglomer- 
ate besides  granite  bowlders  up  to  four  feet  in  diameter.  The 
relations  are  not  very  clear  and  the  till  is  not  certainly  an  entire- 
ly distinct  deposit. 

BREMER  COUNTY. 

No  exposures  were  seen  showing  a  recognizably  distinct,  later 
till  overlying  an  earlier  till.  The  phenomena  are  as  portrayed 
in  the  general  description.-  In  boring  on  a  hill  in  Warren  town- 
ship (Township  92  North,  Kange  13  West,  section  34,  south 


202  THE   IOWAN   DRIFT 

line  of  the  southwest  quarter),  the  following  deposits  were 
penetrated  : 

DBIFT  FIVE  MILES  EAST  OF  WAVERLY,  IOWA. 

FEET 

5     Dark    pebbly    soil    and    yellow    pebbly    clay    till    leached 

(lowan?)     ..............................................        3% 

4.     Till,  yellow,  calcareous  (lowan?)  ..........................    y2 

3.     Ashen-gray,  pebbly  clay  till,  calcareous  ) 


-. 

2.  Ashen-gray,  sandy  till,  calcareous  ____  f 

1.    Yellow',  clayey  till,  calcareous  ............................        1 

Boring  stopped  by  bowlder  or  bedrock. 

There  is  here  a  suggestion  of  a  thin  later  till  overlying  the 
bleached,  but  not  leached,  upper  part  of  a  thin  lower  till.  The 
basis  for  separation  is,  however,  very  slight  and  uncertain. 

PAYETTE  COUNTY. 

So  important  has  a  certain  section  near  Oelwein  been  regarded 
that  it  may  be  well  to  present  here  some  of  the  data  concerning 
it.  The  cut  is  on  the  Chicago  Great  Western  railway,  southeast 
of  Oelwein  (in  Jefferson  township,  Township  91  North,  Range 
9  West,  sections  27  and  28).  When  the  cut  was  seen  by  the 
writers  in  1914  the  sides  were  badly  obscured  by  slumping  and 
vegetation  excepting  in  the  upper  part.  By  digging  at  a  point 
about  200  yards  east  of  the  north-south  viaduct,  the  following 
section  was  made  out  : 

DRIFT  NEAR  OELWEIX,  IOWA. 

FEET 

10.     Black  soil  and  brown  loam  with  occasional  pebbles  ......     1V&-2 

9.     A    line   and   a   lenticular   accumulation    of   pebbles   and 

cobbles  up  to  5  inches  in  diameter  (lens  10  inches  deep 

-    4   feet  long)     ......................................... 

8.  Till,  yellowish  brown,  leached  3%  to  4  feet,  calcareous, 
buff  in  upper  1%  feet  with  mottlings  of  brown,  then 
changes  to  gray  with  less  brown  mottling  for  iy2  feet, 
then  in  lower  6-10  inches  it  becomes  gray-blue  with 
streaks  and  mottlings  of  brown,  total  till  ...............  7-7  'V2 

1.  Humus  clay,  chocolate  brown,  rusty  brown  streak  separat- 
ing 'from  till  above,  leached,  rests  in  basin-like  depres- 
sion, almost  2  feet  thick  at  sides  and  3  feet  in  middle.  .  .  2-3 

6.  Dense  clay,  difficult  to  dig,  no  pebbles  seen  larger  than 
buckahot,  most  of  them  mere  quartz  grains  but  even 
these  rare;  clay  mainly  blue,  but  blue-black  just  below 
soil  ................  .  .................................  3V2-4y2 

5.  Dense  gritty  clay,  occasionally  rotten  greenstone  pebbles 

%  inch  in  diameter,  dark  green  in  color;  leached  ......  1± 

4.  Sandy  clay,  pale  green,  occasionally  a  greenstone  and 

quartz  pebble  1/1  inch  in  diameter;  leached  ............  2-3 

3.  Brown  sandy  clay,  pebbles  up  to  2  inches  in  diameter, 


IOWAN   TILL  AT   OELWEIN  203 

quartzite  and  rotten  granite;    leached   v 

2.     Blue  clay  with  same  kind  of  pebbles  as  above. . .  . . . .  . . .  1 

1.     Sand    and    gravel,    leached,    light    brown,    loose,    rotten 

granite  pebbles  found  in  it,  just  exposed  at  bottom  for y2 

Number  10  does  not  seem  to  be  till  but  an  accumulation  per- 
haps of  wind-blown  dust,  humus,  fine  material  brought  up  by 
burrowing  animals  and  only  an  occasional  pebble  such  as  would 
be  expected  to  be  brought  up  by  them  or  washed  in.  Number  8 
is  not  separable  into  two  tills.  It  is  probably  all  Kansan.  It 
is  true  that  the  upper  six  inches  to  one  foot  is  more  sandy  than 
the  lower  part  and  is  slightly  darker  brown  but  not  more  than 
would  be  expected  from  the  material  that  was  last  deposited  by 
the  ice  and  subjected  to  wash  from  its  waters,  to  later  weather- 
ing and  to  frost  action.  In  places  there  is  a  slight  color  and 
textural  distinction  between  the  leached  portion  and  the  under- 
lying calcareous  part,  but  no  sharp  line  can  be  drawn.  This 
distinction  probably  is  the  result  of  leaching,  leaving  the  leached 
portion  slightly  more  sandy.  Number  7  is  clearly  a  soil  zone 
(Aftonian).  Below  this  the  dense  clays  appear  to  be  silts,  the 
result  of  pond  deposition  and  similar  processes.  Numbers  2 
and  3  may  be  till  but  this  is  by  no  means  clear. 

The  only  indication  seen  by  the  writers  that  the  uppermost 
oxidized  till  might  be  distinct  was  the  presence  at  two  places  of 
three  to  three  and  one-half  feet  of  brown  or  yellow  sand  below 
it.  This  was  traceable  but  a  short  distance  laterally  and  in 
itself  constitutes  only  a  very  slight  basis  (if  any)  for  the  separa- 
tion of  a  post-Kansan  till  sheet. 

In  July,  1907,  E.  T.  Chamberlin  examined  the  exposure.  The 
following  is  from  his  notes  concerning  this  cut: 

There  has  been  so  much  slumping  here  that  much  digging  is 
necessary  before  the  section  can  be  made  out.  According  to  an 
intelligent  railway  foreman  who  was  present  when  the  cut  was 
made  (9  to  10  years  ago)  and  who  had  much  to  do  with  the 
making  of  the  cut,  the  "cut  was  originally  left  as  a  very  steep 
bank  (vertical  steam  shovel  bank)  and  the  present  slope  is  en- 
tirely due  to  slumping  and  wash.  The  section  when  fresh  must 
have  been  a  good  one,  but  at  the  present  time  it  can  only  be 
pieced  together  with  much  digging.  A  section  made  at  a  point 
100  feet  north  of  the  milepost  was  as  follows : 


204  THE   IOWAN   DRIFT 


1.  Kansan  drift.    Upper  8  feet  yellow  brown,  somewhat 
speckled  with  light  grayish  blue  mottlings.     Not  a 
very  hard  clay  here.     The  upper  portion  has  been 
cut  off  by  the  lowan  ice  and  some  of  that  drift  has 
mixed  in.     It  has  been  leached  down  5  feet.     Then 
come  4  feet  of  dark  bluish  hard,  chunky  clay  with 
the   upper   portion    of   it   grading   rapidly   into   the 
brownish  drift  above.     Total  thickness 12 

2.  Aftonian. 

(a)  Red   brown   sand   2-4   in.,   a  highly   oxidized 

interglacial  sand. 

(b)  Layer  of  solid  humus  1  in. 

(c)  Clay     containing     much     vegetable     humus. 

Color  in  upper  portion  dark  reddish  brown 
with  a  lavender  cast;  in  lower  portion  ordi- 
nary rusty  reddish  brown.     Vegetable  mat- 
ter chiefly  in  upper  part.  Total  thickness..          1        2 
Elsewhere   nearby   there    is   some   variation    in    the 
thickness  of  this  colored  clay,  especially  in  its  down- 
ward gradation. 

3.  Sub-Aftonian.     Light  grayish  blue,  hard  clay,  becom- 
ing darker  below.     Contains  very  few  pebbles.  Only 
the  upper  foot  or  two  could  be  seen  even  with  con- 
siderable digging  on   account   of  the   great   amount 
of  wash  material.     Height  of  top  of  this  drift  above 

the  track  8 

J.  Mullin,  the  foreman  who  saw  the  cut  dug  and  who  has  since 
dug  six  feet  below  the  level  of  the  track  to  put  in  tiling,  says  that 
this  clay  becomes  darker  blue  and  much  harder  below,  and  that 
it  extends  as  one  -uniform  formation  to  at  least  six  feet  below 
the  present  level  of  the  tracks. 

Apparently  the  portion  of  the  sub-Aftonian  seen  was  only  the 
top  of  the  unoxidized  material  where,  like  the  Kansan,  it  has 
become  lighter  in  color  but  not  yet  oxidized  to  brown.  The 
clayey  layer  above  (2c)  represents  the  weathered  portion  which 
in  the  upper  part  has  been  modified  by  vegetable  matter.  Above 
this  is  the  solid  humus  layer  representing  the  surface  upon  which 
the  interglacial  gravels  were  laid.  Upon  the  gravels  rests  the 
blue-black  Kansan  till  without  a  soil  line. 

Mr.  Mullin  brought  me  a  slab  of  peaty  material  one  and  one- 
half  feet  in  diameter  and  about  one  inch  thick,  which  came  from 
the  one  inch  humus  layer  when  the  cut  was  first  dug  and  which 
(together  with  much  more  of  the  stuff)  has  lain  on  the  old  dump 
pile  ever  since.  This  breaks  off  in  layers  and  resembles  "old 
leather"  somewhat.  He  has  also  found  fragments  of  wood  at 
this  level. 

[See  Appendix  A,  table  No.  5,  for  estimate  of  pebbles  from 
the  Kansan  drift.] 


IOWAN  TILL  AT  OELWEIN  205 

One  hundred  feet  to  the  south  (at  the  1  milepost)  the  reddish 
brown  Af toman  is  found  in  a  small  gully.  Below  this  is  the 

le  black  till  which  may  be  sub-Aftonian  though  there  is  a 
possibility  that  it  is  Kansan,  the  Aftonian  having  been  incorpor- 
ated in  the  Kansan  ice.  In  some  respects  this  looks  like  a  lens 
of  Aftonian  but  there  is  so  little  of  it  exposed  and  so  much  slope 
wash  about  that  it  is  uncertain. 

It  may  be  called  sub-Aftonian  doubtful  and  classified  as  such. 
There  were  more  pebbles  in  this  than  in  the  topmost  part  of  the 
sub-Aftonian  in  the  last  section. 

[See  Appendix  A,  table  No.  9  for  estimate  of  pebbles  from 
the  sub-Aftonian.] 

Section  at  milepost  [correction  for  upper  part  of  section  de- 
scribed above].  The  upper  five  feet  of  this  section  are  grassed 
and  the  lowan  was  missed,  but  can  be  found  thirty  feet  to  the 
northwest.  At  this  point  are  four  feet  of  yellow  brown,  non- 
calcareous  lowan  drift  which  does  not  break  in  chunks  like  the 
Kansan  and  is  also  fresher  in  appearance.  Below  it  are  two 
inches  of  yellowish  sand.  Then  comes  calcareous,  yellow-brown 
Kansan,  as  described  above.  Hence  Kansan  is  only  seven  feet 
thick  here,  though  elsewhere  in  the  cut  it  is  usually  more  than 
this. 

This  cut  is  through  a  ridge  of  highland  and  hence  (the  topog- 
raphy being  chiefly  pre-Iowan)  was  likely  to  be  subject  to  ero- 
sion by  the  lowan  ice.  This  is  probably  the  reason  why  Kansan 
is  found  to  be  calcareous  up  to  its  top.  The  leached  zone  has 
been  eroded  away. 

[See  Appendix  A,  table  No.  5  for  estimate  of  pebbles  from  the 
Kansan.] 

The  first  cut  two-thirds  mile  from  the  station  shows  the  lowan 
drift  to  better  advantage  than  the  deeper  cut  farther  on,  for  the 
steam  shovel  has  been  in  here  recently.  The  section  is : 

FEET      IN. 

1.  Surface  soil   20 

2.  Yellow-brown  lowan  drift.  More  sandy  than  the  Kansan, 
noncalcareous  throughout 2 

3.  Bright  yellow  Buchanan  interglacial  sand 14 

4.  Kansan  drift,  grayish  brown  to  yellow-brown  just  'be- 
low the  sand.     Calcareous  to  the  very  top.    Lower  por- 
tion buried  under  talus.    To  the  railroad  tracks 1ft 

The  Kansan  is  streaky  in  color  and  breaks  off  in  chunks;  the 
lowan  is  uniform  in  color  and  though  hard  does  not  break  into 
chunks. 

[See  Appendix  A,  table  No.  3  for  estimate  of  pebbles  from  the 
lowan.] 


206  THE   IOWAX   DRIFT 

One  hundred  yards  farther  on  the  lowan  becomes  more  varied 
in  color,  being  yellow,  brown,  and  gray  in  patches.  It  is  very 
hard,  especially  when  dry,  but  does  not  break  in  chunks  like  the 
Kansan.  It  is  noncalcareous. 

The  Buchanan  interglacial  sand  here  becomes  quite  gravelly. 
The  section  is : 

FEET 

1.  Hard,  tenaceous,  yellowish  brown,  or  grayish  brown  (lowan 
drift.     Thickness  including  surface  soil 6 

2.  Buchanan  sands  and  gravels   2-2^ 

3.  Brownish  Kansan  drift  to  tracks 7 

[See  Appendix  A,  table  No.  4  for  estimate  of  pebbles  from  the 
Buchanan  gravel.] 

The  following  is  a  description  by  Prof.  S.  "W.  BeyerGGa  from  an 
examination  of  the  cut  soon  after  the  excavation  was  made. 

Oelwein  Section. — The  cut  on  the  Chicago  Great  "Western  Bail- 
way,  east  of  the  town  of  Oelwein,  in  southern  Fayette  county, 
exhibits  the  following  series  of  glacial  deposits: 

FEET 

5.  Bowlder  clay,  rather  dull-yellow  in  color;  the  upper 
portion  is  modified  into  a  thin  soil  layer.  Large 
bowlders,  mainly  of  the  granitic  type,  are  present, 
often  resting  on  or  partially  imbedded  in  the  de- 
posits lower  in  the  series.  (lowan) 0-10 

4.  Sand    and   gravel — not   a    continuous    deposit;    often 
shows  water  action  expressed  in  parallel  stratifica-     - 
tion  lines  and  false  bedding.    The  gravels  are  usually 
highly  oxidized  and  fine  textured.     (Buchanan)    ....  0-2 

3.  Till,  usually  bright-yellow  above,  graduating  into  a 
gray-blue  when  dry  or  a  dull-blue  when  w'et,  below. 
This  deposit  is  massive  and  exhibits  a  tendency  to 
joint  when  exposed.  Decayed  granitic  bowlders  are 
common.  (Kansan)  3-20 

2.     (a)   Sand,  fine-white,  well  water-worn;,  often  with  a 

slight  admixture  of  silt  and  clay  (Aftonian) 0     6  in. 

(b)  Vegetal  layer  and  soil,  from  two  to  four  inches 
of  almost  pure  carbonaceous  matter,  with  one  to 
three  feet  highly  charged  with  humus.  The  peaty 
layer  often  affords  specimens  of  moss  (Hypnum) 
perfectly  preserved.  (Aftonian) 0-4 

1.     Till,    greenish-blue   when    Wet    or   gray-blue    with   a 
greenish  cast  when  dry.     Greenstones  and  vein  quartz 
pebbles   predominate.      (Sub-Aftonian    or   Albertan.) 
Exposed  10 

"""Beyer,  S.  W.,  Evidence  of  a  sub- Aftonian  till  sheet  in  northeastern  Iowa; 
Proc.  Iowa  Acacl.  Science,  Vol.  IV,  p.  59. 


IOWAN  TILL  AT  OELWEIN  207 


Datum  line 


Vertical  scale  Horizontal  scale 

0  25  50  FEET      500  0  500  FEET 


Figure    15 — Diagram    of    deposits    exposed    in    Chicago    Great    Western    Railway    cut 
southeast   of   Oelwein,    Iowa    (After   Beyer). 

Professor  Beyer  gives  the  above  sketch  of  the  cut  (figure  15). 
Following  the  section  quoted,  Professor  Beyer,  in  his  paper 
which  deals  particularly  with  the  sub-Aftonian  till,  makes  the 
following  statements  concerning  the  lowan : 

The  Oelwein  hill  trends  northwest  and  southeast  and  is 
bilobed.  The  divisions  will  be  referred  to  in  the  present  paper  as 
east  and  \vest  lobes. 

The  lowan  reaches  its  maximum  development  near  the  sum- 
mit of  the  west  lobe,  where  it  attains  a  thickness  of  some  ten  feet. 
The  deposit  thins  eastward.  At  the  crest  of  the  east  lobe  little 
more  than  a  foot  of  lowan  till  is  present,  while  at  the  extreme 
eastern  limit  of  the  cut  lowan  bowlders  are  partially  imbedded 
in  the  Kansan.  The  till  varies  from  a  pale  yellow  to  a  moder- 
ately bright  yellow  color,  and  is  not  thoroughly  leached  nor 
oxidized.  The  lowan  shows  a  tendency  to  crumble  on  exposure, 
which  is  in  striking  contrast  to  the  older  drift  sheets. 

The  line  of  separation  between  the  lowan  and  Kansan  is  not 
as  well  marked,  in  all  cases,  as  could  be  desired,  but  in  most 
instances  can  be  traced  with  some  degree  of  confidence.  In  the 
west  lobe  a  layer  of  sand  sharply  divides  the  two  sheets  for  a 
distance  of  100  feet,  but  when  followed  in  either  direction  be- 
comes much  disarranged  by  the  latter  and  in  some  places  entirely 
loses  its  identity. 

The  Kansan  is  the  predominant  sheet  in  the  cut  and  the 
topographic  features  of  the  region  are  faithfully  depicted  by 
the  stiff  bowlder  clay  of  this  deposit.  Its  maximum  exposure 
is  in  the  east  lobe,  where  it  exhibits  a  thickness  of  twenty  teet 
The  upper  portion  is  oxidized  to  a  bright  yellow,  sometimes 
brownish-yellow,  often  closely  resembling  the  lowan  in  color. 
The  most'  distinctive  feature  in  its  separation  from  the  latter 
is  the  character  of  the  included  bowlders  and  the  greater  t 
nacitv  of  the  Kansan  till.  The  lowan  pebbles  and  bowlders  are 
prevailingly  of  the  granite  type  and  well  preserved,  while  m  the 
Kansan  greenstones  are  common  and  many  of  the  granites  are 


208  THE   IOWAX   DRIFT 

in  an  advanced  state  of  decay.  A  granitic  bowlder  more  than 
a  foot  in  diameter  was  noted  which  had  been  cleaved  by  the 
steam  shovel  without  being  loosened  from  its  matrix.  Sand 
bowlders,  lenses  and  wedges  anomalously  distributed  through 
the  oxidized  portion  and  often  extending  into  the  upper  portion 
of  the  blue  till  are  common  features.  The  wedges  usually  main- 
tain a  more  or  less  vertical  position  with  their  apices  pointing 
downward.  The  filling  material  in  all  cases  closely  resembles  the 
sand  layers  between  the  lowan  and  Kansan.  Oftentimes  the 
position  of  the  various  sand  forms  is  such  as  to  suggest  their 
common  origin  with  the  Buchanan.  In  many  instances  strati- 
fication lines  are  common.  In  the  trough  of  the  hill,  the  lower 
portion  of  the  Kansan  contains  lime  concretions  similar  to  the 
loesskindchen  and  puppchen  in  great  numbers.  The  lower  three 
or  four  feet  of  the  blue  till  contains  wood  fragments  in  consider- 
able abundance  in  a  state  of  almost  perfect  preservation.-  The 
physical  properties  of  this  portion  of  the  Kansan  are  very  simi- 
lar to  the  sub-Aftonian. 

[The  estimates  of  lithologic  character  of  the  pebbles  made  by 
Mr.  Chainberlin  JTOTU  the  lowan  and  Kansan  and  by  Alden  and 
Leigh  ton  from  the  Kansan  do  not  indicate  any  marked  lithologic 
difference  between  the  lowan  and  Kansan  in  this  cut.  See 
Appendix  A,  tables  3  and  5.] 

DELAWARE  COUNTY. 

Doctor  Calvin07  reported  lowan  drift  as  overlying  Buchanan 
gravel  at  scores  of  points  within  the  county.  W  J  McGee"8  re- 
ported the  discovery  of  buried  soil  and  wood  in  wells  in  Greeley 
and  southeast  of  Masonville  in  Prairie  township,  (Township  88 
North,  Range  t>  West,  section  35,  southwest  quarter  of  the  north- 
west quarter),  but  Professor  Calvin  regarded  these  as  belonging 
to  the  Aftonian  horizon.60 

BUCHANAN  COUNTY. 

In  discussing  the  Buchanan  gravel  Doctor  Calvin70  refers  to 
the  county  gravel  pit  near  the  Illinois  Central  railway,  two  miles 
west  of  Winthrop  (Liberty  township,  Township  88  North,  Range 
8  West,  section  4,  northwest  quarter),  and  writes: 

'•Iowa  Geological   Survey,  Vol.  VIII,   p.   170. 

CxTT.    S.   Geol.    Survey   Eleventh   Ann     Kept.,    p.    520. 

69Op.   cit.,   pp.   164-5. 
70Iowa    Geological    Survey,    Vol.    VIII,    p.    242,    1897. 


IQW AN    (?)   TILL  IN  BUCHANAN  COUNTY  209 

The  line  of  division  between  the  gravel  and  the 
overlying  lowan  drift  is  also  well  shown,  and  at  the  south  side 
of  the  pit  there  are  yet  remnants  of  the  interglacial  soil  bed.  The 
lower  ten  feet  ot  the  exposure  is  made  up  of  coarse,  cross-bedded 
sand  which  is  sharply  defined  from  the  still  coarser  gravel  which 
constitutes  the  upper  part  of  the  deposit. 

When  the  pit  was  seen  by  the  writers  in  1914  ail-but  the  upper 
part  of  the  section  was  badly  obscured.  The  upper  part,  how- 
ever, was  clean  in  part  and  showed  the  following: 

DRIFT  Two  MILES  WEST  OF  WINTHROP,  IOWA. 

FEET      IX. 

3.  Dark  brown  porous  loamy  clay  containing  a  few 
pebbles 0_3 

2.  Pebble  layer  very  definite,  looks  somewhat  like  till 

in  places  but  very  thin 0-8 

1.     Rusty  brown  stratified  sand  and  gravel 3-6 

Xo  trace  wTas  seen  of  the  "interglacial  soil"  reported  by 
Doctor  Calvin  above  No.  1. 

Exposures  beside. the  road  one  mile  east  of  Independence 
(Township  88  North,  Range  9  West,  section  2,  northwest  quar- 
ter), where  Doctor  Calvin  found  two  and  one-half  feet  of  lowan 
drift  overlying  Buchanan  gravel,  were  examined  in  1914  and 
showed  the  following: 

DRIFT  ONE  MILE  EAST  OF  INDEPENDENCE,  IOWA. 

FEET 

•2.  Dark  grayish  to  brownish  sandy  loam,  slightly  banded 
and  inclosing  scattered  pebbles,  small  to  six  inches  in 

diameter    %  -2 

1.  Rusty  brown  gravel  with  a  little  sticky,  brown  clay  in- 
termingled. Pebbles  small  to  eight  inches  or  more  in 
diameter,  mostly  less  than  one  inch.  Some  granites 
thoroughly  disintegrated 3 

A  boring  in  the  bottom  of  the  excavation  penetrated: 

FEET 

Brown  gravel 1 

Brown  sand 6 

Buff  sand 1 

Limestone  is  exposed  below  a  thin  covering  of  drift  in  the 
road  a  short  distance  to  the  west  and  limestone  was  struck  at 
a  depth  of  ten  feet  in  drilling  a  nearby  well,  so  that  it  is  prob- 
able that  there  is  but  little  drift  below  the  depth  reached  by  the 
anger,  that  is,  eleven  or  twelve  feet  from  the  original  surface. 
Doctor  Calvin  regarded  No.  1  as  Buchanan  gravel  and  No.  2  as 

14 


210  .  THE   IOWAN   DRIFT 

lowan  drift.     It  is  not  very  certain,  however,  that  the  latter  is 
glacial  till. 

W  J  McGee71  reported  buried  soil  and  wood  as  having  been 
encountered  in  digging  wells  three  miles  north  of  Independence 
in  Washington  township,  (Township  89  North,  Range  9  West, 
section  15,  southwest  quarter  of  the  southeast  quarter  and  in 
section  22,  northeast  quarter  of  the  northeast  quarter). 

BLACK  HAWK  COUNTY. 

Some  exposures  in  Cedar  Falls  not  far  from  the  State  Teach- 
ers College  were  examined.  One  of  these  is  just  north  of  the 
race  track,  in  Township  89  North,  Range  14  West,  section  13, 
southeast  quarter.  This  is  at  a  pit  in  the  big  gravel  deposit  in 
the  valley  of  a  branch  of  Dry  Run.  The  section  is  as  follows : 

DRIFT  ix  SOUTHEAST  PART  OF  CEDAR  FALLS,  IOWA. 

FbET 

3.  Clay,  dark  to  brown,  loamy,  leached,  containing  some 

pebbles.  Till-like  in  part 2%-  3 

2.  Sand  and  gravel,  buff,  stratified  and  cross-bedded, 

leached  4%-  5 

1.  Sand  and  gravel,  calcareous  with  plenty  of  limestone 

pebbles 10± 

While  No.  3  is  till-like  in  part  the  writers  do  not  feel  at  all 
suro  that  it  is  glacial  till.  It  might  be  the  more  poorly  assorted 
part  of  the  alluvial  deposit  laid  down  upon  the  gravels.  The 
gravels  also  are  fresh-looking,  largely  calcareous,  and  but  little 
weathered,  much  less  so  than  the  typical  Buchanan  gravel.  It 
is  possible  these  gravels  may  be  a  part  of  the  Wisconsin  out- 
wash  swept  down  the  Cedar  valley  and  into  the  lower  pavt  of 
Dry  Run  valley,  though  they  may  be  older. 

BENTON  COUNTY. 

A  cut  on  the  Waterloo,  Cedar  Falls  &  Northern  electric  rail- 
way, one  mile  southeast  of  Urbana  in  Polk  township  (Township 
86  North,  Range  9  West,  section  35,  southeast  quarter),  showed 
a  lens  (seven  by  sixteen  feet  in  vertical  section)  of  gravel  above 
and  sand  below,  included  in  solid  buff  to  brown  pebbly  clay  till. 
Fifty  feet  farther  west  six  and  one-half  feet  of  similar  browi? 
gravel  and  sand  was  included  in  the  till.  The  till  is  noncalcare- 
ous  over  the  gravel  but  becomes  calcareous  downward  between 

71U.   S.  Geol.   Survey  Eleventh  Ann.   Rep.,   pp.   489,   519. 


IOWAX   (?)   TILL  IN  LINN  COUNTY  211 

the  two  deposits  at  a  depth  of  eight  or  nine  feet  from  the  top. 
The  relations  shown  in  the  cut  suggest  overriding  of  a  deposit  of 
sand  and  gravel  by  a  readvance  of  the  ice  but  afford  no  good 
evidence  of  a  post-Kansan  till  deposit. 

Only  parts  of  the  county  along  and  near  the  Waterloo,  Cedar 
Falls  &  Northern  railway,  the  Chicago,  Milwaukee  &  St.  Paul 
railway,  and  the  Chicago  &  North  Western  railway  were  ex- 
amined in  1914. 

Professor  T.  E.  Savage72  describes  an  exposure  in  the  east 
bank  of  Mud  creek  in  Taylor  township,  at  the  middle  of  the  west 
line  of  section  27,  which  shows : 

DRIFT    SOUTH    OF   VINTOX,    IOWA. 

FEET 

3.     Fine-grained,  yellow  colored  clay,  containing  no  gravel...     3% 
2.     Bed  of  yelow  drift,  containing  pebbles  and  small  granite 

bowlders  10 

1.     Drift  deposit  which  is  blue  at  the  bottom,  changes  to  a 

yellow  color  higher  up,  and  at  the  very  top  is  a  deep  red. 

This    bed    carries   numerous   pebbles   and   small    bowlders 

of  dark  colored  trap 8 

Number  1  of  the  above  section  represents  Kansan  drift,  the 
upper  part  of  wThieh  presents  the  typical  ferretto  character.  The 
contained  greenstone  pebbles  and  bowlders  are  characteristic 
of  this  ancient  till.  Number  2  is  regarded  as  a  deposit  of  lowan 
drift.  It  is  of  a  uniformly  yellow  color  throughout.  Its  super- 
ficial portion  is  unleached  of  its  calcareous  matter,  and  its  iron 
content  is  not  more  oxidized  in  one  portion  than  another.  The 
bed  here  is  said  to  be  much  thicker  than  is  usual  for  this  till. 
Number  3  is  a.  bed  of  loess. 

LINN  COUNTY.. 

A  possible  exposure  of  lowan  till  was  noted  two  miles  west  of 
Prairiesburg,  in  Boulder  township  (Township  86  North,  Eange 
5  West,  section  20),  near  the  west  line  of  the  bank  of  a  tributary 
of  Buffalo  creek,  where  the  following  was  seen : 

DRIFT   Two  MILES  WEST  OF  PRAIRIESBURG,   IOWA. 

FEET 

4.     Sandy  soil %-!' 

3.     Sand   3 

2.     Brownish    leached    sandy    till    (lowan?) 1-2% 

1.  Gray  to  brown  interstratified  sand  and  gravel,  granite 
pebbles  decayed,  clay  ironstones  present  but  no  lime- 
stone pebbles  remain  5 

"Iowa  Geological   Survey,  Vol.  XV,  p.   207,  1905. 


212  THE   IOWAX   DRIFT 

If  the  sand  and  gravel  (No.  1)  is  Buchanan,  No.  2  might  be 
regarded  as  post-Kansan  though  the  deposit  is  so  very  thin  and 
sandy  that  one  could  hardly  be  certain  that  it  is  glacial  till. 

JOXES  COUNTY. 

Professor  Calvin73  described  an  exposure  in  the  railroad  cut 
just  west  of  Amber,  as  follows : 

DRIFT  WEST  OF  AMEER,  IOWA. 


4-  5 

2.  Till,  yellow,  with  rather  large  pebbles  and  small  bowlders 

(lowan  drift)  10 

1.  Blue  clay  with  small  pebbles,  clay  somewhat  stratified 

(Kansan  drift)    12 

It  seems  not  improbable  that  the  yellow  till  is  merely  the  oxi- 
dized portion  of  the  Kansan  since  there  is  gradation  from  one 
to  the  other  with  no  definite  line  of  demarcation  and  no  evidence 
of  an  interval  of  exposure  between,  such  as  is  afforded  by  the 
soil  and  " gumbo"  bed  found  in  the  exposures  described  on 
page  94  as  present  three  miles  to  the  northwest  in  section  30, 
Wayne  township. 

JSIowa   Geological   Survey,   Vol.   V,   p.    65,   1895. 


t 


Date  Due 


Library  Bureau  Cat.  No.  1137 


